Leetcode#107 Binary Tree Level Order Traversal II

 1 vector<vector<int> > levelOrderBottom(TreeNode *root) {
 2         vector<vector<int> > res;
 3         queue<TreeNode *> layer;
 4         
 5         layer.push(root);
 6         while (!layer.empty()) {
 7             queue<TreeNode *> nextLayer;
 8             vector<int> path;
 9             
10             while (!layer.empty()) {
11                 TreeNode *front = layer.front();
12                 layer.pop();
13                 if (!front)
14                     continue;
15                 path.push_back(front->val);
16                 nextLayer.push(front->left);
17                 nextLayer.push(front->right);
18             }
19             if (path.size() > 0)
20                 res.push_back(path);
21             layer = nextLayer;
22         }
23         
24         vector<vector<int> > tra;
25         for (int i = res.size() - 1; i >= 0; i--)
26             tra.push_back(res[i]);
27             
28         return tra;
29 }