LeetCode --Binary Tree Level Order Traversal II

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<vector<int> > levelOrderBottom(TreeNode *root) {
13         vector<vector<int> > ans;
14         typedef pair<TreeNode*, int> pii;        
15         #define X first
16         #define Y second
17         if (root != NULL) {
18             ans.resize(1);
19             queue<pii> Q;
20             //int level = 0, pre = -1;
21             Q.push(pii(root, 0));
22             while (!Q.empty()) {
23                 
24                 pii cur = Q.front(); Q.pop();
25                 TreeNode *tmp = cur.X;
26                 ans.resize(cur.Y+1);
27                 ans[cur.Y].push_back(tmp->val);
28                 
29                 if (tmp->left != NULL) {
30                     Q.push(pii(tmp->left, cur.Y+1));
31                 }
32                 if (tmp->right != NULL) {
33                     Q.push(pii(tmp->right, cur.Y+1));
34                 }
35             }
36             int len = ans.size();
37             for (int i = 0; i < len/2; i++) {
38                 swap(ans[i], ans[len-i-1]);
39             }
40         }
41         return ans;
42     }
43 };