[leetcode]Balanced Binary Tree

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.

算法思路：

求出各个子树是否是平衡二叉树。为了防止多余计算，最好采取后序遍历。

代码如下：

public class Solution {
   public boolean isBalanced(TreeNode root) {
        if(root == null || (root.left == null && root.right == null))
            return true;
        if(!isBalanced(root.left) || !isBalanced(root.right))
            return false;
        int left = getHeight(root.left);
        int right = getHeight(root.right);
        if(Math.abs(right - left) > 1) return false;
        return true;
    }
    
    private int getHeight(TreeNode root){
        if(root == null) return 0;
        if(root.left == null && root.right == null) return 1;
        int left = 0,right = 0;
        if(root.left != null) left = getHeight(root.left);
        if(root.right != null) right = getHeight(root.right);
        return Math.max(left, right) + 1;
    }
}