110. 平衡二叉树

java:

class Solution {
    public boolean isBalanced(TreeNode root) {
        if (isBalancedCore(root) == -1)
            return false;
        return true;
    }

    public int isBalancedCore(TreeNode root) {
        if (root == null)
            return 0;
        int left = isBalancedCore(root.left);
        int right = isBalancedCore(root.right);
        if (Math.abs(left - right) > 1 ) 
            return -1;
        //注！！发现-1一直返回-1，不然就返回最大深度
        return (left == -1 || right == -1) ? -1 : Math.max(left, right) + 1;
        //return Math.abs(left - right) > 1 ? -1 : Math.max(left, right) + 1这是错的
    }
}