leetCode 107. Binary Tree Level Order Traversal II 二叉树层次遍历反转

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最新推荐文章于 2025-09-12 17:31:31 发布

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原文链接：https://yq.aliyun.com/articles/463182

107. Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree [3,9,20,null,null,15,7],

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

解题思路：

此题与Binary Tree Level Order Traversal相似，只是最后的结果有一个反转。

参考 http://qiaopeng688.blog.51cto.com/3572484/1834819

代码如下：

/**

 * 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:

    vector<vector<int>> levelOrderBottom(TreeNode* root) {

        vector<vector<int>> result;

        queue<TreeNode *> current,next;

        vector<int> level;

        if(NULL == root)

            return result;

        current.push(root);

        while(current.size())

        {

            while(current.size())

            {

                TreeNode *p;

                p = current.front();

                current.pop();

                level.push_back(p->val);

                if(p->left)

                    next.push(p->left);

                if(p->right)

                    next.push(p->right);

            }

            result.push_back(level);

            level.clear();

            swap(current,next);

        }

        reverse(result.begin(),result.end());

        //相对与Binary Tree Level Order Traversal只加了这一句。reverse()，反转

        return result;

    }
};

本文转自313119992 51CTO博客，原文链接:http://blog.51cto.com/qiaopeng688/1834833