Cinte's Leetcode Record
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剑指 Offer 55 - II. 平衡二叉树

Posted on Edited on In Disqus:
Symbols count in article: 1.1k Reading time ≈ 1 mins.

剑指 Offer 55 - II. 平衡二叉树

dfs
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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 {
public:
    bool isBalanced(TreeNode* root) {
        if(!root)
            return true;
        auto left = dfs(root->left);
        auto right = dfs(root->right);
        if(abs(left - right) <= 1 && isBalanced(root->left) && isBalanced(root->right))
            return true;
        return false;
    }
private:
    int dfs(TreeNode* root)
    {
        if(!root)
            return 0;
        return max(dfs(root->left), dfs(root->right)) + 1;
    }
};
剪枝
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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 {
public:
    bool isBalanced(TreeNode* root) {
        return dfs(root) != -1;
    }
private:
    int dfs(TreeNode* root)
    {
        if(!root)
            return 0;
        auto left = dfs(root->left);
        if(left == -1)
            return -1;
        auto right = dfs(root->right);
        if(right == -1)
            return -1;
        if(abs(left - right) > 1)
            return - 1;
        return max(left, right) + 1;
    }
};