LeetCode:Balanced Binary Tree

题目链接

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.

分析：判断一颗二叉树是否是平衡的，dfs递归求解，递归的过程中顺便求得树的高度                                       本文地址

/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == NULL)return true;
        if(height(root) == -1)return false;
        else return true;
    }
    //若root是平衡树，那么返回树的高度，否则返回-1
    int height(TreeNode *root)
    {
        if(root->left == NULL && root->right == NULL)return 1;
        int leftHeight = 0, rightHeight = 0;
        if(root->left)
            leftHeight = height(root->left);
        if(leftHeight == -1)return -1;
        if(root->right)
            rightHeight = height(root->right);
        if(rightHeight == -1)return -1;
        if(abs(leftHeight-rightHeight) > 1)return -1;
        return 1+max(leftHeight, rightHeight);
    }
};

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