easy/110. Balanced Binary Tree.md · hugh_sun/leetcode

**110. Balanced Binary Tree**

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.

**Example 1:**
Given the following tree [3,9,20,null,null,15,7]:
```
    3
   / \
  9  20
    /  \
   15   7
```
Return true.

**Example 2:**
Given the following tree [1,2,2,3,3,null,null,4,4]:
```
       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
```
Return false.

**Solution:**

[https://leetcode.com/submissions/detail/255967559/](https://leetcode.com/submissions/detail/255967559/)
```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) {
        if(root == null)
            return true;
        if(Math.abs(getHeight(root.left) -getHeight(root.right)) < 2) {
            return isBalanced(root.left) && isBalanced(root.right);
        }
        return false;
    }
    public static int getHeight(TreeNode root) {
        if(root == null)
            return 0;
        return Math.max(getHeight(root.left), getHeight(root.right)) + 1;
    }
}
```

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