Two Sum IV

twosumiv/readme.md

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+653. Two Sum IV - Input is a BST
+Easy
+
+Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.
+
+ 
+
+Example 1:
+
+Input: root = [5,3,6,2,4,null,7], k = 9
+Output: true
+
+Example 2:
+
+Input: root = [5,3,6,2,4,null,7], k = 28
+Output: false
+
+ 
+
+Constraints:
+
+    The number of nodes in the tree is in the range [1, 104].
+    -104 <= Node.val <= 104
+    root is guaranteed to be a valid binary search tree.
+    -105 <= k <= 105
+
+

twosumiv/twosumiv.go

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+package twosumiv
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func lookup(node *TreeNode, target int) bool {
+	if node == nil {
+		return false
+	}
+
+	if node.Val == target {
+		return true
+	}
+
+	if target < node.Val {
+		return lookup(node.Left, target)
+	}
+
+	return lookup(node.Right, target)
+}
+
+func recur(node *TreeNode, root *TreeNode, k int) bool {
+	if node == nil {
+		return false
+	}
+	remaining := k - node.Val
+
+	return (remaining != node.Val && lookup(root, remaining)) ||
+		recur(node.Left, root, k) ||
+		recur(node.Right, root, k)
+}
+
+func findTarget(root *TreeNode, k int) bool {
+	return recur(root, root, k)
+}
+
+func FindTarget(root *TreeNode, k int) bool {
+	return findTarget(root, k)
+}

twosumiv/twosumiv_test.go

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+package twosumiv_test
+
+import (
+	"testing"
+
+	ts "git.jxs.me/leetgo/twosumiv"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEmpty(t *testing.T) {
+	var root *ts.TreeNode
+	found := ts.FindTarget(root, 1)
+	require.False(t, found)
+}
+
+func TestShallow(t *testing.T) {
+	root := ts.TreeNode{
+		Val:   5,
+		Left:  &ts.TreeNode{Val: 4},
+		Right: &ts.TreeNode{Val: 6},
+	}
+	found := ts.FindTarget(&root, 10)
+	require.True(t, found)
+}
+
+func TestShallowMissing(t *testing.T) {
+	root := ts.TreeNode{
+		Val:   5,
+		Left:  &ts.TreeNode{Val: 4},
+		Right: &ts.TreeNode{Val: 6},
+	}
+	found := ts.FindTarget(&root, 12)
+	require.False(t, found)
+}
+
+func TestExample1(t *testing.T) {
+	root := ts.TreeNode{
+		Val: 5,
+		Left: &ts.TreeNode{Val: 3,
+			Left:  &ts.TreeNode{Val: 2},
+			Right: &ts.TreeNode{Val: 4}},
+		Right: &ts.TreeNode{Val: 6,
+			Right: &ts.TreeNode{Val: 7}},
+	}
+	found := ts.FindTarget(&root, 9)
+	require.True(t, found)
+}
+
+func TestExample2(t *testing.T) {
+	root := ts.TreeNode{
+		Val: 5,
+		Left: &ts.TreeNode{Val: 3,
+			Left:  &ts.TreeNode{Val: 2},
+			Right: &ts.TreeNode{Val: 4}},
+		Right: &ts.TreeNode{Val: 6,
+			Right: &ts.TreeNode{Val: 7}},
+	}
+	found := ts.FindTarget(&root, 28)
+	require.False(t, found)
+}
+
+func TestHalf(t *testing.T) {
+	root := ts.TreeNode{
+		Val: 5,
+		Left: &ts.TreeNode{Val: 3,
+			Left:  &ts.TreeNode{Val: 2},
+			Right: &ts.TreeNode{Val: 4}},
+		Right: &ts.TreeNode{Val: 6,
+			Right: &ts.TreeNode{Val: 7}},
+	}
+	found := ts.FindTarget(&root, 14)
+	require.False(t, found)
+}