Add: Balanced Binary Tree

Author: openset

Diff for: problems/balanced-binary-tree/README.md

@@ -16,9 +16,11 @@
 <p>For this problem, a height-balanced binary tree is defined as:</p>
 
 <blockquote>
-<p>a binary tree in which the depth of the two subtrees of <em>every</em> node never differ by more than 1.</p>
+<p>a binary tree in which the left and right subtrees of <em>every</em> node differ in height by no more than 1.</p>
 </blockquote>
 
+<p>&nbsp;</p>
+
 <p><strong>Example 1:</strong></p>
 
 <p>Given the following tree <code>[3,9,20,null,null,15,7]</code>:</p>

Diff for: problems/balanced-binary-tree/balanced_binary_tree.go

@@ -1 +1,38 @@
-package balanced_binary_tree
+package problem_110
+
+import "github.com/openset/leetcode/internal/kit"
+
+type TreeNode = kit.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func isBalanced(root *TreeNode) bool {
+	_, isBalanced := recur(root)
+	return isBalanced
+}
+
+func recur(root *TreeNode) (int, bool) {
+	if root == nil {
+		return 0, true
+	}
+	leftDepth, leftIsBalanced := recur(root.Left)
+	rightDepth, rightIsBalanced := recur(root.Right)
+	if leftIsBalanced && rightIsBalanced &&
+		-1 <= leftDepth-rightDepth && leftDepth-rightDepth <= 1 {
+		return max(leftDepth, rightDepth) + 1, true
+	}
+	return 0, false
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

Diff for: problems/balanced-binary-tree/balanced_binary_tree_test.go

@@ -1 +1 @@
-package balanced_binary_tree
+package problem_110