[Leetcode][Tree][Balanced Binary Tree]

判断一棵树是不是平衡二叉树，之前做过，还有点印象，用一个函数返回树的高度，如果是-1的话，就说明子树不平衡。

1A很开心~

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int height(TreeNode * root) {
        int hleft, hright;
        hleft = hright = 0;
        if (root->left != NULL) {
            hleft = height(root->left);
        }
        if (root->right != NULL) {
            hright = height(root->right);
        }
        if (hleft < 0 || hright < 0 || abs(hleft - hright) > 1) {
            return -1;
        }
        return max(hleft, hright) + 1;
    }
    bool isBalanced(TreeNode *root) {
        if (root == NULL) {
            return true;
        } else {
            return height(root) >= 0;
        }
    }
};