chore: add hackerrank solutions

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
+}