leetcode题解-110-平衡二叉树

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题目

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/**
 * 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 {
private:
    int helper(const TreeNode* root, int level, bool& res)
    {
        if (!root)  return level;

        int lH = helper(root->left, level + 1, res);
        if (!res)   return level;

        int rH = helper(root->right, level + 1, res);
        if (!res)   return level;

        if (abs(lH - rH) > 1)    res = false;

        return max(lH, rH);    
    }
public:
    bool isBalanced(TreeNode* root) 
    {
        bool res = true;

        helper(root, 1, res);
        return res;
    }
};

要保证返回当前结点的 树高 和 是否平衡。