LeetCode题解之Binary Tree Level Order Traversal II

1、题目描述

2、题目分析

先遍历，再反转。

3、代码

 1 vector<vector<int>> levelOrderBottom(TreeNode* root) {
 2         vector<vector<int>> ans;
 3         if (root == NULL)
 4             return ans;
 5         
 6         queue<TreeNode*> q;
 7         q.push(root);
 8         vector<int> v;
 9         while (!q.empty()) {
10             int size = q.size();
11             for (int i = 0; i < size; i++) {
12                 TreeNode *node = q.front();
13                 q.pop();
14                 v.push_back(node->val);
15                 if (node->left != NULL)
16                     q.push(node->left);
17                 
18                 if (node->right != NULL)
19                     q.push(node->right);
20             }
21             ans.push_back(v);
22             v.clear();
23         }
24         
25         reverse(ans.begin(), ans.end());
26         return ans;
27     }