[Leetcode] Balanced Binary Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        int j = treeDepth(root);
        if(j == -1) return false;
        else return true;

        
    }
    int treeDepth(TreeNode* root){
        if(root){
            int m = treeDepth(root->left);
            int n = treeDepth(root->right);
            if(m == -1 || n == -1) return -1;
            if(m-n<=1 && n-m<= 1){
                return m>n?m+1:n+1;
            }
            else return -1;
        }
        else return 0;
    }
    
};

利用遞歸計算每一個節點的子樹深度，然後比較子樹深度之差，如果大於1 返回-1，否則返回其深度， 返回值爲-1說明該子樹不是平衡二叉樹