LeetCode 107. 二叉树的层次遍历 II

/**
 * 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<int> getval(vector<TreeNode*> u){
        vector<int>path;
        for(auto x:u)
            path.push_back(x->val);
        return path;
    }
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        vector<vector<int>>ans;
        if(!root)return ans;
        vector<TreeNode*>level;
        level.push_back(root);
        ans.push_back(getval(level));
        while(true){
            vector<TreeNode*>nl;
            for(auto u:level){
                if(u->left)nl.push_back(u->left);
                if(u->right)nl.push_back(u->right);
            }
            if(nl.size()){
                ans.push_back(getval(nl));
                level=nl;
            }
            else
                break;
            
        }
        reverse(ans.begin(),ans.end());
        return ans;
    }
};