Leetcode-二叉树的层次遍历 II

22.二叉树的层次遍历 II

题目内容：

代码及思路：

/**
 * 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) {
        //按照层遍历最后反向颠倒就可以了
        vector<int> midres;
        vector<vector<int>> res;
        deque<TreeNode*> dequeTreenode;
        dequeTreenode.push_back(root);
        TreeNode* pNode;
        if(root==nullptr)
            return res;
        while(dequeTreenode.size())
        {
            int size=dequeTreenode.size();
            midres.clear();
            for(int i=0;i<size;i++)
            {
                pNode=dequeTreenode.front();
                midres.push_back(pNode->val);
                dequeTreenode.pop_front();
                if(pNode->left)
                    dequeTreenode.push_back(pNode->left);
                if(pNode->right)
                    dequeTreenode.push_back(pNode->right);
                
            }
            res.push_back(midres);
        }
        reverse(res.begin(),res.end());
        
        return res;
    }
};