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

/**
 * 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<int> row;
        vector<vector<int>> v;
        if(root == NULL) {
            return v;
        }
        queue<TreeNode *> q;
        q.push(root);
        TreeNode *temp;
        while(!q.empty()) {
            int size = q.size();
            while(size--) {
                temp = q.front();
                q.pop();
                row.push_back(temp->val);
                if(temp->left != NULL) {
                    q.push(temp->left);
                }
                if(temp->right != NULL) {
                    q.push(temp->right);
                }
            }
            v.insert(v.begin(), row);
            row.clear();
        }
        
        return v;
    }
};

/**

* 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<int> row;

vector<vector<int>> v;

if(root == NULL) {

return v;

}

queue<TreeNode *> q;

q.push(root);

TreeNode *temp;

while(!q.empty()) {

int size = q.size();

while(size--) {

temp = q.front();

q.pop();

row.push_back(temp->val);

if(temp->left != NULL) {

q.push(temp->left);

}

if(temp->right != NULL) {

q.push(temp->right);

}

v.insert(v.begin(), row);

row.clear();

}

return v;

}

};

❤ 点击这里 -> 订阅《PAT | 蓝桥 | LeetCode学习路径 & 刷题经验》by 柳婼

❤ 点击这里 -> 订阅《从放弃C语言到使用C++刷算法的简明教程》by 柳婼

❤ 点击这里 -> 订阅PAT甲级乙级、蓝桥杯、GPLT天梯赛、LeetCode题解离线版