Leetcode: Balanced Binary Tree

来源：互联网发布：mysise php爬虫编辑：程序博客网时间：2024/06/08 05:49

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.

最straight-forward的想法：

/** * 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) {        if (root == NULL) {            return true;        }                if (isBalanced(root->left) && isBalanced(root->right)){            int left_depth = maxDepth(root->left);            int right_depth = maxDepth(root->right);            if (abs(left_depth - right_depth) <= 1) {                return true;            }        }                return false;    }        int maxDepth(TreeNode *root) {        if (root == NULL) {            return 0;        }                return (max(maxDepth(root->left), maxDepth(root->right)) + 1);    }};

检查平衡之后还要计算深度，有些复杂，虽然能通过。能集成到一起吗？

class Solution {public:    bool isBalanced(TreeNode *root) {        int depth = 0;        return checkBalance(root, depth);    }        bool checkBalance(TreeNode *root, int& depth) {        if (root == NULL) {            depth = 0;            return true;        }                int left_depth = 0;        int right_depth = 0;        if (checkBalance(root->left, left_depth) && checkBalance(root->right, right_depth)) {            if (abs(left_depth - right_depth) > 1) {                return false;            }            else {                depth = max(left_depth, right_depth) + 1;                return true;            }        }                return false;    }};

奇怪的是运行时间竟然一样。。。

=======================第二次===========================

/** * 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) {        int depth;        return balance_util(root, depth);    }        bool balance_util(TreeNode* root, int& depth) {        if (root == NULL) {            depth = 0;            return true;        }                int left_depth, right_depth;        if (balance_util(root->left, left_depth) && balance_util(root->right, right_depth)) {            if (abs(left_depth - right_depth) > 1) {                return false;            }            else {                depth = max(left_depth, right_depth) + 1;                return true;            }        }                return false;    }};

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