diff --git a/aoc_test.go b/aoc_test.go
index e12e7a9..b617447 100644
--- a/aoc_test.go
+++ b/aoc_test.go
@@ -78,3 +78,16 @@ func TestList(t *testing.T) {
 
 	is.Equal(a, 5)
 }
+
+func TestGraph(t *testing.T) {
+	g := aoc.Graph[int, uint](7)
+	g.AddEdge(0, 1, 2)
+	g.AddEdge(0, 2, 6)
+	g.AddEdge(1, 3, 5)
+	g.AddEdge(2, 3, 8)
+	g.AddEdge(3, 4, 10)
+	g.AddEdge(3, 5, 15)
+	g.AddEdge(4, 6, 2)
+	g.AddEdge(5, 6, 6)
+	// g.Dijkstra(0)
+}
diff --git a/day07/input2.txt b/day07/input2.txt
new file mode 100644
index 0000000..f6011eb
--- /dev/null
+++ b/day07/input2.txt
@@ -0,0 +1,1000 @@
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\ No newline at end of file
diff --git a/day17/example.txt b/day17/example.txt
new file mode 100644
index 0000000..3c85086
--- /dev/null
+++ b/day17/example.txt
@@ -0,0 +1,13 @@
+2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533
\ No newline at end of file
diff --git a/day17/input.txt b/day17/input.txt
new file mode 100644
index 0000000..04b77c2
--- /dev/null
+++ b/day17/input.txt
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+241355115114515145351235241342577311663523713245571552423844478483444456674576776374774635321762611146175633416417526461446534624524525232351
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+322324544333135432235125224253374616723165212337472223432464246434784434268261665524555163346167575177573432151165141342526636661664333152245
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+142421541514212154334545211465656444644552463442357616615277117635256363621723512341776351424463622726131565431516465664346151153212233245553
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+344341433553215433332561124312211661162315615567541645475225431414323527474442612165214546553775576346352241352363416414626442233143123431324
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+221234522113214232242154165523542235561622643243233434644217742623556626525264626677654256257462621433131425222466152534235213545112335523443
diff --git a/day17/main.go b/day17/main.go
new file mode 100644
index 0000000..57e6617
--- /dev/null
+++ b/day17/main.go
@@ -0,0 +1,214 @@
+package main
+
+import (
+	"bufio"
+	_ "embed"
+	"fmt"
+	"sort"
+
+	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) {
+	var m Map
+
+	for scan.Scan() {
+		text := scan.Text()
+		m = append(m, []rune(text))
+	}
+
+	result := result{}
+	result.valuePT1 = search(m, 1, 3)
+	result.valuePT2 = search(m, 4, 10)
+
+	return &result, nil
+}
+
+var (
+	ZERO = point{0, 0}
+
+	UP = point{-1, 0}
+	DN = point{1, 0}
+	LF = point{0, -1}
+	RT = point{0, 1}
+
+	INF = int(^uint(0) >> 1)
+)
+
+type Map [][]rune
+
+func (m *Map) Get(p point) (point, int, bool) {
+	if !m.Valid(p) {
+		return [2]int{0, 0}, 0, false
+	}
+
+	return p, int((*m)[p[0]][p[1]] - '0'), true
+}
+func (m *Map) GetNeighbor(p point, d point) (point, int, bool) {
+	return m.Get(p.add(d))
+}
+func (m *Map) Size() (int, int) {
+	if m == nil || len(*m) == 0 {
+		return 0, 0
+	}
+	return len(*m), len((*m)[0])
+}
+func (m *Map) Neighbors(p point) []point {
+	var lis []point
+	for _, d := range []point{UP, DN, LF, RT} {
+		if p, _, ok := m.GetNeighbor(p, d); ok {
+			lis = append(lis, p)
+		}
+	}
+	return lis
+}
+func (m *Map) NeighborDirections(p point) []point {
+	var lis []point
+	for _, d := range []point{UP, DN, LF, RT} {
+		if m.Valid(p.add(d)) {
+			lis = append(lis, d)
+		}
+	}
+	return lis
+}
+func (m *Map) Valid(p point) bool {
+	rows, cols := m.Size()
+	return p[0] >= 0 && p[0] < rows && p[1] >= 0 && p[1] < cols
+}
+
+type memo struct {
+	h int
+	s int
+	p point
+	d point
+}
+
+func (memo) sort(a, b memo) bool {
+	if a.h != b.h {
+		return a.h < b.h
+	}
+
+	if a.s != b.s {
+		return a.s < b.s
+	}
+
+	if a.p != b.p {
+		return a.p.less(b.p)
+	}
+
+	return a.d.less(b.d)
+}
+
+type priorityQueue[T any, U []T] struct {
+	elems U
+	sort  func(a, b T) bool
+}
+
+func PriorityQueue[T any, U []T](sort func(a, b T) bool) *priorityQueue[T, U] {
+	return &priorityQueue[T, U]{sort: sort}
+}
+func (pq *priorityQueue[T, U]) Enqueue(elem T) {
+	pq.elems = append(pq.elems, elem)
+	sort.Slice(pq.elems, func(i, j int) bool { return pq.sort(pq.elems[i], pq.elems[j]) })
+}
+func (pq *priorityQueue[T, I]) IsEmpty() bool {
+	return len(pq.elems) == 0
+}
+func (pq *priorityQueue[T, I]) Dequeue() (T, bool) {
+	var elem T
+	if pq.IsEmpty() {
+		return elem, false
+	}
+
+	elem, pq.elems = pq.elems[0], pq.elems[1:]
+	return elem, true
+}
+
+func heuristic(m Map, p point) int {
+	rows, cols := m.Size()
+	return rows - p[0] + cols - p[1]
+}
+
+func search(m Map, minSize, maxSize int) int {
+	rows, cols := m.Size()
+	END := point{rows - 1, cols - 1}
+
+	visited := make(map[vector]int)
+	pq := PriorityQueue(memo{}.sort)
+	pq.Enqueue(memo{h: heuristic(m, point{0, 0}), p: point{0, 0}, d: DN})
+	
+	for !pq.IsEmpty() {
+		mem, _ := pq.Dequeue()
+		fmt.Println(mem)
+		if mem.h > dmap(visited, vector{mem.p[0], mem.p[1], mem.d[0], mem.d[1]}, INF) {
+			continue
+		}
+
+		if mem.p == END {
+			return mem.s
+		}
+
+		for _, nd := range m.NeighborDirections(mem.p) {
+			if nd[0] == 0 && mem.d == RT || nd[1] == 0 && mem.d == DN {
+				continue
+			}
+
+			dscore := 0
+
+			for _, size := range irange(1, maxSize+1) {
+				np := mem.p.add(nd.scale(size))
+				_, s, ok := m.Get(np)
+
+				if !ok {
+					break
+				}
+
+				dscore += s
+				pscore := mem.s + dscore
+
+				nh := heuristic(m, np) + pscore
+				vec := vector{np[0], np[1], nd[0], nd[1]}
+
+				if size >= minSize && nh < dmap(visited, vec, INF) {
+					pq.Enqueue(memo{nh, pscore, np, nd})
+					visited[vec] = nh
+				}
+			}
+		}
+	}
+
+	return 0
+}
+
+func dmap[K comparable, V any](m map[K]V, k K, d V) V {
+	if v, ok := m[k]; ok {
+		return v
+	}
+	return d
+}
+func irange(a, b int) []int {
+	lis := make([]int, b-a)
+	for i := range lis {
+		lis[i] = i + a
+	}
+	return lis
+}
+
+type point [2]int
+
+func (p point) add(a point) point { return point{p[0] + a[0], p[1] + a[1]} }
+func (p point) scale(m int) point { return point{p[0] * m, p[1] * m} }
+func (p point) less(a point) bool { return p[0] < a[0] || p[1] < a[1] }
+
+type vector [4]int
diff --git a/day17/main_test.go b/day17/main_test.go
new file mode 100644
index 0000000..d7fd635
--- /dev/null
+++ b/day17/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, 102)
+	is.Equal(result.valuePT2, 94)
+}
+
+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, 843)
+	is.Equal(result.valuePT2, 1017)
+}
diff --git a/day20/example1.txt b/day20/example1.txt
new file mode 100644
index 0000000..9ed10dd
--- /dev/null
+++ b/day20/example1.txt
@@ -0,0 +1,5 @@
+broadcaster -> a, b, c
+%a -> b
+%b -> c
+%c -> inv
+&inv -> a
\ No newline at end of file
diff --git a/day20/example2.txt b/day20/example2.txt
new file mode 100644
index 0000000..4da4379
--- /dev/null
+++ b/day20/example2.txt
@@ -0,0 +1,5 @@
+broadcaster -> a
+%a -> inv, con
+&inv -> b
+%b -> con
+&con -> output
\ No newline at end of file
diff --git a/day20/input.txt b/day20/input.txt
new file mode 100644
index 0000000..c2efe97
--- /dev/null
+++ b/day20/input.txt
@@ -0,0 +1,58 @@
+%vg -> lf, vd
+%dr -> kg
+%cn -> mv, pt
+%rq -> bk, gr
+%vp -> lp, bk
+%kg -> lv
+%lv -> jc, tp
+%sj -> rm, vd
+%jc -> tp, qr
+%km -> tp, dr
+%jx -> cn
+&vd -> tf, lf, nb, cx, hx, lr
+%lp -> jt, bk
+%vj -> ps
+broadcaster -> km, lr, xh, rf
+%dj -> pt, gc
+%cg -> vd, hx
+&ln -> tg
+%fl -> pt, sk
+%lm -> tr, bk
+%lr -> vd, vg
+&pt -> vq, rf, cm, jx, rg
+%cx -> gp
+%gp -> vd, sj
+&db -> tg
+%st -> vd
+%jt -> bk
+%jh -> lm, bk
+%xf -> bd, tp
+%gc -> cm, pt
+&tp -> dr, km, kg, db, vj, qr
+%ps -> xf, tp
+%rf -> pt, dj
+%lf -> nb
+%bd -> tp, gg
+%dk -> tp, vj
+%mn -> jh, bk
+&tg -> rx
+%ql -> bk, zx
+%tr -> bk, vp
+%sk -> pt
+%nb -> cg
+%sb -> vd, cx
+%qr -> dk
+%xh -> bk, ql
+%rg -> sd
+%hx -> sb
+%sd -> pt, jx
+%gr -> bk, mn
+%gg -> tp
+%zx -> rq
+&bk -> xh, ln, zx
+%rm -> st, vd
+%hq -> fl, pt
+&vq -> tg
+%cm -> rg
+&tf -> tg
+%mv -> pt, hq
diff --git a/day20/main.go b/day20/main.go
new file mode 100644
index 0000000..fdcd47c
--- /dev/null
+++ b/day20/main.go
@@ -0,0 +1,282 @@
+package main
+
+import (
+	"bufio"
+	_ "embed"
+	"fmt"
+	"strings"
+
+	aoc "go.sour.is/advent-of-code"
+	"golang.org/x/exp/maps"
+)
+
+// 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) {
+	m := &machine{}
+	receivers := make(map[string][]string)
+
+	for scan.Scan() {
+		text := scan.Text()
+
+		name, text, _ := strings.Cut(text, " -> ")
+		dest := strings.Split(text, ", ")
+
+		switch {
+		case name == "broadcaster":
+			m.Add(name, &broadcaster{dest: dest})
+		case strings.HasPrefix(name, "%"):
+			name = strings.TrimPrefix(name, "%")
+			m.Add(name, &flipflop{name: name, dest: dest})
+
+		case strings.HasPrefix(name, "&"):
+			name = strings.TrimPrefix(name, "&")
+			m.Add(name, &conjunction{name: name, dest: dest})
+		}
+
+		for _, d := range dest {
+			// rx is present so enable pt 2
+			if d == "rx" {
+				m.Add("rx", &rx{})
+			}
+			receivers[d] = append(receivers[d], name)
+		}
+	}
+
+	m.setup(receivers)
+
+	result := &result{}
+
+	for i := 0; i < 10_000; i++ { // need enough presses to find the best LCM values for each conjunction
+		if i == 1000 {
+			result.valuePT1 = m.highPulses * m.lowPulses
+		}
+		m.Push(i)
+	}
+
+	// rx is present.. perform part 2.
+	if rx, ok := receivers["rx"]; ok {
+		tip := m.m[rx[0]].(*conjunction) // panic if missing!
+
+		var lvalues []int
+		for k, v := range tip.pushes {
+			for i, h := range makeHistory(v) {
+				if i == 1 && len(h) > 0 && h[0] > 0 {
+					fmt.Println(tip.name, k, "frequency", h[0])
+					lvalues = append(lvalues, h[0])
+				}
+			}
+		}
+
+		result.valuePT2 = aoc.LCM(lvalues...)
+		fmt.Println(tip.name, "LCM", result.valuePT2, lvalues)
+	}
+	return result, nil
+}
+
+type signal bool
+
+const (
+	LOW  signal = false
+	HIGH signal = true
+)
+
+type message struct {
+	signal
+	from, to string
+}
+
+type machine struct {
+	m map[string]pulser
+
+	queue []message
+
+	press      int
+	highPulses int
+	lowPulses  int
+}
+
+func (m *machine) Add(name string, p pulser) {
+	if m.m == nil {
+		m.m = make(map[string]pulser)
+	}
+	p.SetMachine(m)
+	m.m[name] = p
+}
+func (m *machine) Send(msgs ...message) {
+	m.queue = append(m.queue, msgs...)
+	for _, msg := range msgs {
+		// fmt.Println(msg)
+		if msg.signal {
+			m.highPulses++
+		} else {
+			m.lowPulses++
+		}
+	}
+}
+func (m *machine) Push(i int) {
+	m.press = i
+	m.Send(generate(LOW, "button", "broadcaster")...)
+	m.processQueue(i)
+}
+func (m *machine) processQueue(i int) {
+	// look for work and process up to the queue length. repeat.
+	hwm := 0
+	for hwm < len(m.queue) {
+		end := len(m.queue)
+
+		for ; hwm < end; hwm++ {
+			msg := m.queue[hwm]
+
+			if p, ok := m.m[msg.to]; ok {
+				// fmt.Println(i, "S:", m.m[msg.from], msg.signal, "R:", p)
+				p.Pulse(msg)
+			}
+		}
+
+		hwm = 0
+		copy(m.queue, m.queue[end:])
+		m.queue = m.queue[:len(m.queue)-end]
+		// fmt.Println("")
+	}
+}
+func (m *machine) setup(receivers map[string][]string) {
+	for name, recv := range receivers {
+		if p, ok := m.m[name]; ok {
+			if p, ok := p.(interface{ Receive(...string) }); ok {
+				p.Receive(recv...)
+			}
+		}
+	}
+}
+
+type pulser interface {
+	Pulse(message)
+	SetMachine(*machine)
+}
+
+// IsModule implements the machine registration for each module.
+type IsModule struct {
+	*machine
+}
+
+func (p *IsModule) SetMachine(m *machine) { p.machine = m }
+
+type broadcaster struct {
+	dest []string
+	IsModule
+}
+
+func (b *broadcaster) Pulse(msg message) {
+	b.Send(generate(msg.signal, "broadcaster", b.dest...)...)
+}
+
+type flipflop struct {
+	name  string
+	state signal
+	dest  []string
+
+	IsModule
+}
+
+func (b *flipflop) Pulse(msg message) {
+	if !msg.signal {
+		b.state = !b.state
+		b.Send(generate(b.state, b.name, b.dest...)...)
+	}
+}
+
+type conjunction struct {
+	name  string
+	state map[string]signal
+	dest  []string
+
+	pushes map[string][]int
+
+	IsModule
+}
+
+func (b *conjunction) Receive(names ...string) {
+	if b.state == nil {
+		b.state = make(map[string]signal)
+		b.pushes = make(map[string][]int)
+	}
+	for _, name := range names {
+		b.state[name] = false
+		b.pushes[name] = []int{}
+	}
+}
+func (b *conjunction) Pulse(msg message) {
+	b.state[msg.from] = msg.signal
+
+	if msg.signal {
+		// collect frequency of pushes to esti,ate rate
+		b.pushes[msg.from] = append(b.pushes[msg.from], b.press)
+	}
+
+	if all(HIGH, maps.Values(b.state)...) {
+		b.Send(generate(LOW, b.name, b.dest...)...)
+		return
+	}
+	b.Send(generate(HIGH, b.name, b.dest...)...)
+}
+
+type rx struct {
+	IsModule
+}
+
+func (rx *rx) Pulse(msg message) {
+	if !msg.signal {
+		panic("pulse received") // will never happen...
+	}
+}
+
+// helper funcs
+func all[T comparable](match T, lis ...T) bool {
+	for _, b := range lis {
+		if b != match {
+			return false
+		}
+	}
+
+	return true
+}
+func generate(t signal, from string, destinations ...string) []message {
+	msgs := make([]message, len(destinations))
+	for i, to := range destinations {
+		msgs[i] = message{signal: t, from: from, to: to}
+	}
+	return msgs
+}
+
+// makeHistory from day 9
+func makeHistory(in []int) [][]int {
+	var history [][]int
+	history = append(history, in)
+
+	// for {
+	var diffs []int
+
+	current := history[len(history)-1]
+
+	for i := range current[1:] {
+		diffs = append(diffs, current[i+1]-current[i])
+	}
+
+	history = append(history, diffs)
+
+	// if len(diffs) == 0 || aoc.Max(diffs[0], diffs[1:]...) == 0 && aoc.Min(diffs[0], diffs[1:]...) == 0 {
+	// 	break
+	// }
+	// }
+	return history
+}
diff --git a/day20/main_test.go b/day20/main_test.go
new file mode 100644
index 0000000..1ab6824
--- /dev/null
+++ b/day20/main_test.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+
+	_ "embed"
+
+	"github.com/matryer/is"
+)
+
+//go:embed example1.txt
+var example1 []byte
+
+//go:embed example2.txt
+var example2 []byte
+
+//go:embed input.txt
+var input []byte
+
+func TestExample1(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(example1))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 32000000)
+	is.Equal(result.valuePT2, 0)
+}
+
+func TestExample2(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(example2))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.valuePT1, 11687500)
+	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, 819397964)
+	is.Equal(result.valuePT2, 252667369442479)
+}
diff --git a/math.go b/math.go
index 468b1d6..b6d1124 100644
--- a/math.go
+++ b/math.go
@@ -2,8 +2,14 @@ package aoc
 
 import "cmp"
 
+type uinteger interface {
+	uint | uint8 | uint16 | uint32 | uint64
+}
+type sinteger interface {
+	int | int8 | int16 | int32 | int64
+}
 type integer interface {
-	int | int8 | int16 | int32 | int64 | uint | uint8 | uint16 | uint32 | uint64
+	sinteger | uinteger
 }
 
 // type float interface {
diff --git a/search.go b/search.go
new file mode 100644
index 0000000..8a8eea8
--- /dev/null
+++ b/search.go
@@ -0,0 +1,103 @@
+package aoc
+
+import (
+	"sort"
+)
+
+type PQElem[T any, I integer] struct {
+	Value    T
+	Priority I
+}
+type PQList[T any, I integer] []PQElem[T, I]
+
+func (pq PQList[T, I]) Len() int {
+	return len(pq)
+}
+func (pq PQList[T, I]) Less(i int, j int) bool {
+	return pq[i].Priority < pq[j].Priority
+}
+func (pq PQList[T, I]) Swap(i int, j int) {
+	pq[i], pq[j] = pq[j], pq[i]
+}
+
+var _ sort.Interface = (*PQList[rune, int])(nil)
+
+type PriorityQueue[T any, I integer] struct {
+	elem PQList[T, I]
+}
+
+func (pq *PriorityQueue[T, I]) Enqueue(elem T, priority I) {
+	pq.elem = append(pq.elem, PQElem[T, I]{elem, priority})
+	sort.Sort(pq.elem)
+}
+func (pq *PriorityQueue[T, I]) IsEmpty() bool {
+	return len(pq.elem) == 0
+}
+func (pq *PriorityQueue[T, I]) Dequeue() (T, bool) {
+	var elem T
+	if pq.IsEmpty() {
+		return elem, false
+	}
+
+	elem, pq.elem = pq.elem[0].Value, pq.elem[1:]
+	return elem, true
+}
+
+type Vertex[V comparable, I integer] struct {
+	to    V
+	score I
+}
+type graph[V comparable, I uinteger] struct {
+	adj map[V][]Vertex[V, I]
+}
+
+func Graph[V comparable, I uinteger](size int) *graph[V, I] {
+	return &graph[V, I]{
+		adj: make(map[V][]Vertex[V, I], size),
+	}
+}
+func (g *graph[V, I]) AddEdge(u, v V, w I) {
+	g.adj[u] = append(g.adj[u], Vertex[V, I]{to: v, score: w})
+	g.adj[v] = append(g.adj[v], Vertex[V, I]{to: u, score: w})
+}
+func (g *graph[V, I]) Dijkstra(m interface{ Get() }, src V) map[V]I {
+	pq := PriorityQueue[V, I]{}
+	dist := make(map[V]I, len(g.adj))
+	visited := make(map[V]bool, len(g.adj))
+	var INF I
+	INF = ^INF
+
+	pq.Enqueue(src, 0)
+	dist[src] = 0
+
+	for !pq.IsEmpty() {
+		u, _ := pq.Dequeue()
+
+		if _, ok := visited[u]; ok {
+			continue
+		}
+		visited[u] = true
+
+		for _, v := range g.adj[u] {
+			_, ok := visited[v.to]
+			var du, dv I
+			if d, inf := dist[u]; !inf {
+				du = INF
+			} else {
+				du = d
+			}
+			if d, inf := dist[v.to]; !inf {
+				dv = INF
+			} else {
+				dv = d
+			}
+
+			if !ok && du+v.score < dv {
+				dist[v.to] = du + v.score
+				pq.Enqueue(v.to, du+v.score)
+			}
+		}
+	}
+
+	return dist
+}