feat: add 110

Author: Blankj

README.md

@@ -30,7 +30,8 @@
 |101|[Symmetric Tree][101]|Tree, Depth-first Search, Breadth-first Search|
 |104|[Maximum Depth of Binary Tree][104]|Tree, Depth-first Search|
 |107|[Binary Tree Level Order Traversal II][107]|Tree, Breadth-first Search|
-|108|[Binary Tree Level Order Traversal II][107]|Tree, Depth-first Search|
+|108|[Convert Sorted Array to Binary Search Tree][108]|Tree, Depth-first Search|
+|110|[Balanced Binary Tree][110]|Tree, Depth-first Search|
 
 
 ## Medium

note/101/README.md

@@ -51,7 +51,7 @@ class Solution {
         return root == null || isSymmetricHelper(root.left, root.right);
     }
 
-    public boolean isSymmetricHelper(TreeNode left, TreeNode right) {
+    public boolean helper(TreeNode left, TreeNode right) {
         if (left == null || right == null) return left == right;
         if (left.val != right.val) return false;
         return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left);

note/110/README.md

@@ -0,0 +1,52 @@
+# [Balanced Binary Tree][title]
+
+## Description
+
+Given a binary tree, determine if it is height-balanced.
+
+For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
+
+**Tags:** Tree, Depth-first Search
+
+
+## 思路
+
+题意是判断一棵二叉树是否是高度平衡的，所谓二叉树高度平衡指的是二叉树的每个节点的两棵子树的高度差都不超过1。
+
+
+``` java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public boolean isBalanced(TreeNode root) {
+        return helper(root) != -1;
+    }
+
+    private int helper(TreeNode node) {
+        if (node == null) return 0;
+        int l = helper(node.left);
+        if (l == -1) return -1;
+        int r = helper(node.right);
+        if (r == -1) return -1;
+        if (Math.abs(l - r) > 1) return -1;
+        return 1 + Math.max(l, r);
+    }
+}
+```
+
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我GitHub上的LeetCode题解：[awesome-java-leetcode][ajl]
+
+
+
+[title]: https://leetcode.com/problems/balanced-binary-tree
+[ajl]: https://github.com/Blankj/awesome-java-leetcode

project/leetcode/.idea/workspace.xml

@@ -18,7 +18,7 @@ public class Solution {
 //        return root == null || isSymmetricHelper(root.left, root.right);
 //    }
 //
-//    private boolean isSymmetricHelper(TreeNode left, TreeNode right) {
+//    private boolean helper(TreeNode left, TreeNode right) {
 //        if (left == null || right == null) return left == right;
 //        if (left.val != right.val) return false;
 //        return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left);

project/leetcode/out/production/leetcode/com/blankj/easy/_110/Solution.class

@@ -0,0 +1,33 @@
+package com.blankj.easy._110;
+
+
+import com.blankj.structure.TreeNode;
+
+/**
+ * <pre>
+ *     author: Blankj
+ *     blog  : http://blankj.com
+ *     time  : 2017/10/09
+ *     desc  :
+ * </pre>
+ */
+public class Solution {
+    public boolean isBalanced(TreeNode root) {
+        return helper(root) != -1;
+    }
+
+    private int helper(TreeNode node) {
+        if (node == null) return 0;
+        int l = helper(node.left);
+        if (l == -1) return -1;
+        int r = helper(node.right);
+        if (r == -1) return -1;
+        if (Math.abs(l - r) > 1) return -1;
+        return 1 + Math.max(l, r);
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.isBalanced(TreeNode.createTestData("[1,2,2,3,3,3,3,4,4,4,4,4,4,null,null,5,5]")));
+    }
+}