leetcode 107. Binary Tree Level Order Traversal II

最新推荐文章于 2025-09-13 14:08:34 发布

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最新推荐文章于 2025-09-13 14:08:34 发布

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分类专栏： leetcode 文章标签： leetcode 107

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本文介绍了一种从叶节点到根节点的层次遍历二叉树的方法，并提供了一个具体的C++实现示例。

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],
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[
[15,7],
[9,20],
[3]
]

class Solution {
public:
        
    vector<vector<int>> levelOrderBottom(TreeNode* root) 
    {
        vector<vector<int>> ret;
        if (!root)
            return ret;
            
        queue<TreeNode*> que;
        que.push(root);
        
        while (!que.empty())
        {
            int size = que.size();
            vector<int> temp;
            for (int i = 0; i < size; i++)
            {
                TreeNode *p = que.front();
                que.pop();
                temp.push_back(p->val);
                if (p->left)
                    que.push(p->left);
                if (p->right)
                    que.push(p->right);
            }
            ret.push_back(temp);
        }
        reverse(ret.begin(), ret.end());
        return ret;
    }
};