leetcode 107.Binary Tree Level Order Traversal II 二叉树的层次遍历 II

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 /**
  * 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) {
         if(root==NULL) return {};
         queue<TreeNode*> q;
         TreeNode* front;
         q.push(root);
         vector<vector<int>> res;
         while(!q.empty()){
             vector<int> onelevel;
             for(int i=q.size();i>;i--){
                 front=q.front();
                 q.pop();
                 if(front->left)
                     q.push(front->left);
                 if(front->right)
                     q.push(front->right);
                 onelevel.push_back(front->val);
             }
             res.push_back(onelevel);
         }
         reverse(res.begin(),res.end());
         return res;
     }
 };

其实这个解答只是reverse 了一下，算是投机取巧吧，之后写个从叶节点遍历的。