110. Balanced Binary Tree——beats 100.00% of javascript submissions.

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.

我的想法是使用递归，将根节点传人，如果这个节点判断左右子树是不是平衡树，如果不是就返回－1，是就继续判断这个跟节点所在的子树是不是平衡树（左右子树深度绝对值小于2），如果不是返回－1，如果是返回 左右子树深的那个的深度加一（代表本颗子树的深度）。

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    if (!root) 
        return true;
    var howmany = function(root) {
        var left = 0;
        var right = 0;
        if (root.left) 
            left = howmany(root.left);
        if (root.right)
            right = howmany(root.right);
        if ((left>=0)&&(right>=0)) {
            if (Math.abs(left-right)>1) {
                return -1;
            } else {
                return left>right ? left+1 : right+1;
            }
        }
        return -1;
        
    }
    return howmany(root)<0 ? false : true;
};

这里写图片描述