leetCode 110. Balanced Binary Tree 平衡二叉樹

110. Balanced Binary Tree

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.

題目大意：

判斷一顆二叉樹是否爲平衡二叉樹。

思路：

1. 作一個輔助函數來求的樹的高度。

2. 經過輔助函數來遞歸求解。

代碼以下：

/**
 * 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:
    int depth(TreeNode* root)
    {
        if(!root)
            return 0;
        int l = depth(root->left) ;
        int r = depth(root->right) ;
        return 1 + ((l > r)?l:r);
    }
    bool isBalanced(TreeNode* root) {
        if(!root)
            return true;
        else
        {
            int l = depth(root->left);
            int r = depth(root->right);
            if(l + 1 < r || r + 1 <l)
            {
                return false;
            }
            else
                return (isBalanced(root->left) && isBalanced(root->right) );
        }
    }
};

2016-08-08 00:25:26