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>0;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。