110. Balanced Binary Tree

可以在调用链回归时进行比较以避免重复计算深度。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    boolean balanced=true;
    public boolean isBalanced(TreeNode root) {
            balanceHelper(root);
            return balanced;
    }
    private int balanceHelper(TreeNode root)
    {
        if(root==null) return 0;
        int right =  balanceHelper(root.right);
        int left =   balanceHelper(root.left);
        if(Math.abs(right-left)>1)
            balanced=false;
        return left>right?left+1:right+1;

    }
}