(BFS 简单) Leetcode 107. 二叉树的层次遍历 II

跟102,103的思路一样，也是用空间换时间。

/**
 * 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) {
        vector<vector<int>>result;
        if(root==nullptr)
            return result;
        queue<TreeNode*>que;
        que.push(root);
        while(!que.empty())
        {
            vector<int>vec;
            vector<TreeNode*>vec_que;
            
            while(!que.empty())
            {
                root=que.front();
                que.pop();
                vec.push_back(root->val);
                if(root->left)
                    vec_que.push_back(root->left);
                if(root->right)
                    vec_que.push_back(root->right);
            }
            result.push_back(vec);
            vec.clear();
            for(int i=0;i<vec_que.size();i++)
            {
                que.push(vec_que[i]);
            }
        }
        vector<vector<int>>rresult;
        for(int j=result.size()-1;j>=0;j--)
        {
            rresult.push_back(result[j]);
        }
        return rresult;

    }
};