LeetCode——Balanced Binary Tree

pickless

于 2013-09-22 01:22:08 发布

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分类专栏： Online Judge 文章标签： leetcode

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本文介绍了一种判定二叉树是否为高度平衡的方法。高度平衡的二叉树定义为对于每个节点，其两个子树的深度之差不超过1。通过递归地计算每个节点的左右子树高度并比较，来实现这一判定。

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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 ofevery node never differ by more than 1.

» Solve this problem

依题意，直接判断左右子树高度差是否不超过1.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    bool balanced = true;
    
    int height(TreeNode *root) {
        if (!balanced) {
            return -1;
        }        
        if (root == NULL) {
            return 0;
        }
        int lH = height(root->left) + 1;
        int lL = height(root->right) + 1;
        if (abs(lH - lL) > 1) {
            balanced = false;
        }
        return lH > lL ? lH : lL;
    }
    
public:
    bool isBalanced(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        balanced = true;
        height(root);
        return balanced;
    }
};