chore: add hackerrank solutions

README.md.sig

@@ -0,0 +1,6 @@
+-----BEGIN SSH SIGNATURE-----
+U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgZ+OuJYdd3UiUbyBuO1RlsQR20a
+Qm5mKneuMxRjGo3zkAAAAEZmlsZQAAAAAAAAAGc2hhNTEyAAAAUwAAAAtzc2gtZWQyNTUx
+OQAAAED8T4C6WILXYZ1KxqDIlVhlrAEjr1Vc+tn8ypcVM3bN7iOexVvuUuvm90nr8eEwKU
+acrdDxmq2S+oysQbK+pMUE
+-----END SSH SIGNATURE-----

aoc2023/day21/example.txt

@@ -0,0 +1,11 @@
+...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........

aoc2023/day21/input.txt

@@ -0,0 +1,131 @@
+...................................................................................................................................
+.#.......#..#...#.......#......#....#..#...#...#....#.#..........................................#...............#..........#......
+.............##..................#......#.#....#.......................##..#........................#......#..........#............
+......#..........................#....#.....#.............#................##....#.#.............#.........#.##...........#........
+.#................#............................#...........................#..##.....#..................#..##..#.#.........##......
+.....#.............#.....##.............##..........#...........#.............#.....#...........#.#.......#....#......#..........#.
+........#....................#....#.#.#......##........#...........#...........#..........#...#..........#......................#..
+.........#.#...#.......#........#........##...#...#..##........................................##...#.#........................#...
+......#.....#..#..#.#..#..............#...#..#.....#...........#.....#........#.#...........#...........#.#...............#.....#..
+...........#.......####..#.#..............##................#.#.#.....................##.....................#...#..............#..
+......###...#......#................##...#...#....#...........#...#..............#.........#..#..................................#.
+...............#..##..........#...........................##......#.##.........................#..#.#...........#.#...........#....
+...##........#...#...#...##...##...........#..#...................#...................#.#..#.........#.......#..#...........##...#.
+................#.....#..##......#.....#.....##............#..#..........##...........................#.#.......##.....#.....#.....
+.#..#.......#.#...#..##.....#............................#......#...#....#................#.#..#.....#.......##................#...
+...............#.....#........................#..........#.....#..............................................#..................#.
+.....#......#..........................................#....................................#..#.......#.#..#......#.#....#..##....
+............##............#.......###.......................#..#....#......................................#..#.........#..........
+..#...............#.....#...#...#......................#...#.#..............................#.#..#.#.....#.#.#..#....#.....#...##..
+.#.............................##.................#.......#.......##....#....................#.....#.#........#.....#........#.....
+.#....##...................##.....#.#..............#.#....#....#..#....#......#..........#.....##............#....#.............##.
+.........#....#.....#..#.........#....#.#..........#...#...#.......#....#..##.......................#.#..#........#..#....#..#.#...
+..#..................#.......#..#.#..............##.......#........#..............#.........#..#....#......#..#..........#.........
+........#.....#......#.....#......#...#.......#....#.......#.#..#................#....................##.............#.......#.....
+..#.................#..............#...........................................#.....#..................#...#.#..................#.
+.......#......#.....#...........................#.....#..................#.....................#.....#.#......#........#.#.......#.
+..#.#.#...................#...#..#................#....#.......#......................#...............#.........##...#.#.....###...
+.....#...#....##....#........####...........#.................#...#...........................................#..............##....
+..##.#..#.#..........#.#.#..#................................#..#.............#..#......#...........................#.##...........
+..............#.............................##........#..##........................#.............................#........#........
+........#.........#........#..#........#..#........#...#.#........#...........#.........................#.#..........#...#......#..
+.........##.....#........#.....................#..#.............#.....#........#....................#....#.#.#......#.....#........
+......................#...................####..#.........#....#.........#...........#..................#..#.................#.....
+..#.........#...#.....##................##.##....#.....#....#..............................#..#.............#..#...................
+..........##......#..#..............#.#....#......#................#.....#....#..............#..................#..................
+.#.#..####...#....................#.#.#.....#...#...................#....#.#.....#.#.......#.#...........#......#.#................
+.......#.........#..#.#..............###.......#....#.........................#.......#.###...#............#....#.#..#....###.#....
+........#....#...#......#.................#..........................#.........................#...........##.............#.#......
+.#..............#.....................#......#.............##............#..#..........#...................#...#....#..............
+......#..#..#.#...............#........###.......#.#...........#...........#.#.........#..#.....................#......#..#.#......
+.....#...............#.........#....#..........#.......#.......#......#...#..##.....#.....#........#.#.......#.......#..#...#......
+..#............#.....................#...#.......#....###...........#.....#.#.................#................#.........#..##.#...
+..............................#.....#..................................#.....##...............#.......#.........#.....#....##......
+..#...##...#...#..............#.................##..#......#.................#....#......#...#...#......#..........................
+.........#....#..............#........#..#...............#....#...#.....#..#......#.........#.......#.#..#........#...........#....
+........#..#....................#.........#...##.#.#..............#......#.#..........##...##....#......................#..........
+.##..#....#....#.......##......#............#..#......#.....##..................#####..#...#......#.#...#..........#.#.....#..#....
+..#...........#....................#.......#......#.........#...............#......#........##........#.................#.....#.#..
+..#....#.#...............#.#.........................#.............####..............................##................###.........
+.....#.......................................#....#...##...#.......#.......#.....#.##..##.................#.....................##.
+.........#...........#..#..##.#..........#..#.........#..#.....#...................................##....#...............#..#.#....
+.....#..#...........##............#........#..................#............#..........#..........#..#...........#..................
+............................#.........#...............#..................#.#....#.#..#........#.....#...........#...........#......
+................#...##.#....#..##..........#.#........##.#..#..#.....................#....#.................#.#...............#....
+.#.....#..............#.#..........#..#........#...............#..#.#..##..#.#.#.........................#.................#.......
+....#..............#................#.....#..#.......#..#.#.........#..........#..........#.....#..........##.....#............#...
+..............##...........#.......#......#..................#.......#.....#.#...#...............#.#........#......#............#..
+................#.....#....#........#....#.......#.#.##.....#...#..#.##...#................#.#.....#....#.............#............
+...........#.#.##..####.....#....#.#...#.#...........#...#.......................#.#....#.....#..#................###..............
+...................#....#..........#.#..##.....#..#..#......###............#..#...........#....#......#............................
+...........................................#.......#..............#.##.......##.......#...#.....#.#..#.....#..###..................
+............###........#.......#.#....#.....#....#..#........#.........##....#.....#..........#......#............#..#.#...........
+............#..........#................##.#..............#.....#................#....................................#..#.........
+...........#.....#.....................#...#.....#.......#..........#....#.....###.....##.#.##.#.....#......#......#.......#.......
+.....................#..#.....#...##.....#..#...........#....#....##............##.................##............##................
+.................................................................S.................................................................
+........#.#........#..........#.....#......#........#.#............#.#.........##...#............#...#.....#...........#.....#.....
+..................##.......#......#..#..................#..##......#.........#...#.........#............#....#...........##........
+..................#...........#.##.......#..............#....................#.#....#...##...#.....#.......#..#.....##.............
+...........#....#....##...#................................#.........#.................#....#.......................#...#..........
+.............#.#.#.....#.#...#.......#.#...........#....#.#.........#........##......#.......#.......##...#..........#.##..........
+...........##.#....#....#..#.....#...............#......................#...........#.....#...........#.#.......#..................
+.#.......................#.#...##.#....#.#...........#.#....##.##......#........................##....#.#....#.....................
+...#..................#.#...........##....###.................#....................##......#.....#............#.##....#.......##...
+.#..................####...#.#..#.##.#...####...#......#....................#..........................#....#......................
+.....#..........#.....#.#...............#.........##...#......#.#.....#...........#.....#............##......#.....#...............
+......#........#....#..#............................###.#...##........#........#.................#..#........#...............##....
+......................#.........................##....#...#..............#..#............#.#....#......##.#......#.........##......
+..................#....#...#.#.......#..............#..#..#...#.......#...#.....#.....#...............#.#.#...............#........
+...#...##......................##..##...........#......#.............#............#...........##.......#....#......................
+.............................##...........##...#...#.....#....#.......#.#..#.....##...............#..#.#......#..............##....
+...#..#.#...#.......#..................#............#....#.#.##.#.........#......#........#..#..........#....##...........#....#...
+.....#.............................#......#.#.....#.##.#.................#.........#..#..#.#.#........................#.#.......#..
+....#........#........#....#.#.#.....#.##............###.#..........#...##......#........##...#.........#.............#........#...
+..#..............................#.............................#......#...................#...#......#.............#...............
+.......#...#...............#.................##....................#....##.......#....##....##...#..................#..............
+.........................#...#..#.....##.............#...##.......#.....#...#..............#.....#.#.#..#........................#.
+......#.......##.#.............#....................#...#...........#...#..##....#.....#............#...........#........#.........
+...#....#...#......#........................#.....#.........#......#........#.....#.#...........#.#..............#......#....#.....
+........#..........#...................#...........##.#..#...#................#....##.............#................#....#..........
+........#.......#....#.............#..........#...................#.#....#.#........#..#..............................#..........#.
+............#........#....................#.#.........#......#.............#................#...#.............#....#...............
+..#..............................#..#....##.....#......................##...#..#.........#......#......................#...#...#.#.
+.##....#.............#...........##..................#...#..............#.......#................................#.........#.......
+.....#......#.#.....##...........#.....#.......#..........##..#.............#.#.........#.#.#.............##........#......#..#....
+.......#.......#.#.#..#......................#....#............##....#...........#.........................#......#................
+.........##.........#..............#.#.#....#...#.......#.................................#..##..................##.###.##...#.....
+......................#...#.#.......#..#.#..........#........#.......#.................#..................................#........
+....##........#.........#.........................#................#......#...#.....#..................................#..#.#......
+...##..............#..................#...#......#........###..#.......#..........#..............................#......#..........
+.#.#.#....#..........#......#.#.........#.....#...............................#.....#.#............#....#........#.............#...
+........#.........#.........#......................#..#......##.....#..#..........................#......##....#......##.##.....#..
+.##...#.......#.#....#..#.#...................#.........#....#...........#.....#.........#............##......#............#.......
+.##..#.........#..........#.#.................................#.#.#...............................#............#......##...#.#.....
+......#........#..#...#............#..............#............#......##.....#.................................#......#.#.....#....
+..........#........#...........#....................................#.....#...............................#............##....#.##..
+........#.............#..#......##..................#.............#..#...#.#.....#...#...............#........................#....
+....#...............#..........#....#...........................#....##.##...................#.#.......#...#.##....#........##..#..
+......#.....#..#..........###...#.................####.###..........#...........#..........#......#............................#...
+.#...#......#........#..#............##...............#.##......#...#.....#....................#.........#............#...#........
+................##...................#.##..............#...#..#.......#.......###........#..#..#........#...##.....................
+..............#....#..#..#.............##..............#................................#.....#..#....###.##..............#........
+..#..............#........................................#..........#.....#..................#............#..#....................
+.........#...#.....#...#...##...........#.###............##...#........#......................##......#....#.......#...............
+....#....#.....#.......#......................................#.#.#....#..#..#..........#...................#........#...#.........
+..#..#..................#..............#...#..#.........#......#....#.#................##..........#..#................#...........
+...#...................#...........#....#...#.............##...#.......#.#..........#..#...............#....#....#.............#...
+.......................##.#.#..##........#....#.........#.#.#.....##..............#.......#.......##.#..........#.#................
+.....#..#..................#..##....#.......#.............#...#.....#.............#.............#.#...............#.....##......##.
+...#.#.....#..........#.#............#..#..........................##.............#....#.......#.#...#...#....................#.#..
+............##.#............#....#....#....#..##...#...............................#...#...#.........#.......................##.##.
+....#.#...............#...#.......#............#..#...........................#..............#..........#....#...#...#..#...#....#.
+.......#..#..#.#..#......#..........................#...............#.........#...........#................#..#...#................
+...#..#...#.....#.#.......#....................................................#........#..........#.#...#......#..........#.......
+..#...#.......#..#..............#.#...#.....#...#....#............#..........##...#.........##.............#.......................
+...#.............#...#....#...#.....#.#.#..............#..........#........#........##...........#..#.#......................#.....
+.#.......#.................#...............#..........#.....................#.....#............#......##....#.....#...#....###.....
+...##...........#..........#.#........#............#..#.#........................#.....##............#...##.#.......#.##....#......
+...........#........#...........#.......#......#...#.....#............................#........#..#................#...#....##.....
+...##.##.........#.####..#............#..#.....#.......................#......#..........#.#..#.#....##........#....#.....#..#..##.
+...................................................................................................................................

aoc2023/day21/main.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"bufio"
+	_ "embed"
+	"fmt"
+
+	aoc "go.sour.is/advent-of-code"
+)
+
+// var log = aoc.Log
+
+func main() { aoc.MustResult(aoc.Runner(run)) }
+
+type result struct {
+	valuePT1 int
+	valuePT2 int
+}
+
+func (r result) String() string { return fmt.Sprintf("%#v", r) }
+
+func run(scan *bufio.Scanner) (*result, error) {
+
+	for scan.Scan() {
+		_ = scan.Text()
+
+	}
+
+	return &result{}, nil
+}

aoc2023/day21/main_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+
+	_ "embed"
+
+	"github.com/matryer/is"
+)
+
+//go:embed example.txt
+var example []byte
+
+//go:embed input.txt
+var input []byte
+
+func TestExample(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(example))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 0)
+	is.Equal(result.valuePT2, 0)
+}
+
+func TestSolution(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(input))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 0)
+	is.Equal(result.valuePT2, 0)
+}

aoc2024/day01/main.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"bufio"
+	_ "embed"
+	"fmt"
+
+	aoc "go.sour.is/advent-of-code"
+)
+
+// var log = aoc.Log
+
+func main() { aoc.MustResult(aoc.Runner(run)) }
+
+type result struct {
+	valuePT1 int
+	valuePT2 int
+}
+
+func (r result) String() string { return fmt.Sprintf("%#v", r) }
+
+func run(scan *bufio.Scanner) (*result, error) {
+
+	for scan.Scan() {
+		_ = scan.Text()
+
+	}
+
+	return &result{}, nil
+}

aoc2024/day01/main_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+
+	_ "embed"
+
+	"github.com/matryer/is"
+)
+
+//go:embed example.txt
+var example []byte
+
+//go:embed input.txt
+var input []byte
+
+func TestExample(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(example))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 0)
+	is.Equal(result.valuePT2, 0)
+}
+
+func TestSolution(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(input))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 0)
+	is.Equal(result.valuePT2, 0)
+}

aoc_test.go

@@ -9,66 +9,6 @@ import (
 	aoc "go.sour.is/advent-of-code"
 )
 
-func TestReverse(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.Reverse([]int{1, 2, 3, 4}), []int{4, 3, 2, 1})
-}
-
-func TestLCM(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.LCM([]int{}...), 0)
-	is.Equal(aoc.LCM(5), 5)
-	is.Equal(aoc.LCM(5, 3), 15)
-	is.Equal(aoc.LCM(5, 3, 2), 30)
-}
-
-func TestReadStringToInts(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.ReadStringToInts([]string{"1", "2", "3"}), []int{1, 2, 3})
-}
-
-func TestRepeat(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.Repeat(5, 3), []int{5, 5, 5})
-}
-
-func TestPower2(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.Power2(0), 1)
-	is.Equal(aoc.Power2(1), 2)
-	is.Equal(aoc.Power2(2), 4)
-}
-
-func TestABS(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(aoc.ABS(1), 1)
-	is.Equal(aoc.ABS(0), 0)
-	is.Equal(aoc.ABS(-1), 1)
-}
-
-func TestTranspose(t *testing.T) {
-	is := is.New(t)
-
-	is.Equal(
-		aoc.Transpose(
-			[][]int{
-				{1, 1},
-				{0, 0},
-				{1, 1},
-			},
-		),
-		[][]int{
-			{1, 0, 1},
-			{1, 0, 1},
-		},
-	)
-}
 
 func TestList(t *testing.T) {
 	is := is.New(t)
@@ -116,23 +56,6 @@ func TestPriorityQueue(t *testing.T) {
 	is.True(v == nil)
 }
 
-func TestSet(t *testing.T) {
-	is := is.New(t)
-
-	s := aoc.Set(1, 2, 3)
-	is.True(!s.Has(0))
-	is.True(s.Has(1))
-	is.True(s.Has(2))
-	is.True(s.Has(3))
-	is.True(!s.Has(4))
-
-	s.Add(4)
-	is.True(s.Has(4))
-
-	items := s.Items()
-	sort.Ints(items)
-	is.Equal(items, []int{1, 2, 3, 4})
-}
 
 func ExamplePriorityQueue() {
 	type memo struct {
@@ -194,26 +117,6 @@ func ExamplePriorityQueue() {
 	// point 5 is 22 steps away.
 	// point 6 is 19 steps away.
 }
-
-func TestStack(t *testing.T) {
-	is := is.New(t)
-
-	s := aoc.Stack(1, 2, 3, 4)
-	is.True(!s.IsEmpty())
-	is.Equal(s.Pop(), 4)
-	is.Equal(s.Pop(), 3)
-	is.Equal(s.Pop(), 2)
-	is.Equal(s.Pop(), 1)
-	is.True(s.IsEmpty())
-	s.Push(4, 3, 2, 1)
-	is.True(!s.IsEmpty())
-	is.Equal(s.Pop(), 1)
-	is.Equal(s.Pop(), 2)
-	is.Equal(s.Pop(), 3)
-	is.Equal(s.Pop(), 4)
-	is.True(s.IsEmpty())
-}
-
 func TestGraph(t *testing.T) {
 	is := is.New(t)
 

go.mod

@@ -1,8 +1,6 @@
 module go.sour.is/advent-of-code
 
-go 1.21.4
-
-toolchain go1.21.5
+go 1.23.2
 
 require (
 	github.com/matryer/is v1.4.1

grids.go

@@ -2,7 +2,11 @@ package aoc
 
 import (
 	"cmp"
+	"fmt"
 	"sort"
+	"strings"
+
+	"golang.org/x/exp/maps"
 )
 
 type Vector struct {
@@ -82,6 +86,76 @@ func (m *Map[I, T]) Valid(p Point[I]) bool {
 	return p[0] >= 0 && p[0] < rows && p[1] >= 0 && p[1] < cols
 }
 
+type cmap[C number, N comparable] struct {
+	base      pather[C, N]
+	neighbors map[N]map[N]C
+}
+
+func (m *cmap[C, N]) Cost(a, b N) C {
+	if v, ok := m.neighbors[a]; ok {
+		return v[b]
+	}
+	return 0
+}
+func (m *cmap[C, N]) Neighbors(n N) []N {
+	if v, ok := m.neighbors[n]; ok {
+		return maps.Keys(v)
+	}
+	return nil
+}
+func (m *cmap[C, N]) Target(n N, c C) bool {
+	return m.base.Target(n, c)
+}
+func (m *cmap[C, N]) String() string {
+	var b = &strings.Builder{}
+
+	for k, nbs := range m.neighbors {
+		fmt.Fprintln(b, k)
+		for to, c := range nbs {
+			fmt.Fprintln(b, "  ", to, c)
+		}
+	}
+
+	return b.String()
+}
+
+func CompressMap[C number, N comparable](p pather[C, N], start N) pather[C, N] {
+	var next = []N{start}
+	var visited = make(map[N]map[N]C)
+
+	var n N
+	for len(next) > 0 {
+		n, next = next[len(next)-1], next[:len(next)-1]
+
+		if _, ok := visited[n]; ok {
+			continue
+		}
+
+		nbs := p.Neighbors(n)
+		if len(nbs) == 2 {
+			a, b := nbs[0], nbs[1]
+			if to, ok := visited[a]; ok {
+				to[b] = to[n] + p.Cost(n, b)
+				delete(to, n)
+				visited[a] = to
+			} else if to, ok := visited[b]; ok {
+				to[a] = to[n] + p.Cost(n, a)
+				delete(to, n)
+				visited[b] = to
+			}
+			continue
+		}
+
+		visited[n] = make(map[N]C)
+		next = append(next, nbs...)
+		for _, to := range nbs {
+			visited[n][to] = p.Cost(n, to)
+		}
+	}
+
+	return &cmap[C, N]{base: p, neighbors: visited}
+}
+
 type adjacencyList[V any, C comparable] map[C][]V
 type graph[V any, W cmp.Ordered, C comparable] map[C]*vertex[V, W]
 type graphOption[V any, W cmp.Ordered, C comparable] func(g *graph[V, W, C])
@@ -117,7 +191,7 @@ func Graph[V any, W cmp.Ordered, C comparable](opts ...graphOption[V, W, C]) *gr
 	return &g
 }
 func (g *graph[V, W, C]) AddVertex(id C, value V) {
-	(*g)[id] = &vertex[V,W]{Value: value}
+	(*g)[id] = &vertex[V, W]{Value: value}
 }
 func (g *graph[V, W, C]) AddEdge(from, to C, w W) {
 	if g == nil {
@@ -130,7 +204,7 @@ func (g *graph[V, W, C]) AddEdge(from, to C, w W) {
 		return
 	}
 
-	(*g)[from].Edges = append((*g)[from].Edges, edge[V,W]{(*g)[to], w})
+	(*g)[from].Edges = append((*g)[from].Edges, edge[V, W]{(*g)[to], w})
 }
 func (g *graph[V, W, C]) Neighbors(v C) []V {
 	if g == nil {
@@ -170,5 +244,3 @@ func WithAdjacencyList[W cmp.Ordered, C comparable](list adjacencyList[C, C]) gr
 		}
 	}
 }
-
-// func GraphFromMap()

hacker-rank/binary-search-tree-lowest-common-ancestor/main.go

@@ -0,0 +1,84 @@
+package main
+import (
+    "fmt"
+    "os"
+    "bufio"
+    "strings"
+    "strconv"
+)
+func main() {
+    //Enter your code here. Read input from STDIN. Print output to STDOUT
+    scanner := bufio.NewScanner(os.Stdin)
+    
+    var nodes int
+    var tree *node
+    var target [2]int
+    
+    for scanner.Scan() {
+        text := scanner.Text()
+        if nodes == 0 {
+            nodes, _ = strconv.Atoi(text)
+            continue
+        }
+        
+        if tree == nil {
+            for _, s := range strings.Fields(text) {
+                v, _ := strconv.Atoi(s)
+                tree = insertNode(tree, &node{value:v})
+            }
+            continue
+        }
+        
+        for i, s := range strings.Fields(text) {
+            v, _ := strconv.Atoi(s)
+            target[i] = v
+        }
+    }
+    if target[0]>target[1] {
+        target[0], target[1] = target[1], target[0]
+    }
+    fmt.Fprintln(os.Stderr, tree)
+    if n := lsa(tree, target); n != nil {
+        fmt.Println(n.value)
+        return
+    }
+    fmt.Println("nil")
+}
+
+type node struct{
+    value int
+    left *node
+    right *node
+}
+func insertNode(root, n *node) *node {
+    if root == nil {
+        return n
+    }
+    if root.value > n.value {
+        root.left = insertNode(root.left, n)
+        return root
+    }
+    root.right = insertNode(root.right, n)
+    return root
+}
+
+func (n *node) String() string {
+    if n == nil { return "nil" }
+    return fmt.Sprintf("%v (%v %v)", n.value, n.left, n.right)
+}
+
+func lsa(tree *node, target [2]int) *node {
+    if tree == nil {
+        return nil
+    }
+    
+    if target[0]>tree.value {
+        return lsa(tree.right, target)
+    }
+    
+    if target[1]<tree.value {
+        return lsa(tree.left, target)
+    }
+    
+    return tree
+}