LeetCode107.二叉树的层次遍历II

题目

class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        auto levelOrder = vector<vector<int>> ();
        if(root == NULL ) 
            return levelOrder;
        queue<TreeNode*>q;
        q.push(root);
        while(!q.empty()){
            int num = q.size();
            auto level = vector<int> ();
            while(num > 0){
                TreeNode* p = q.front();q.pop();level.push_back(p->val);
                if(p->left != NULL) q.push(p->left);
                if(p->right != NULL) q.push(p->right);
                num--;   
            }
            levelOrder.push_back(level);
        }
        reverse(levelOrder.begin(),levelOrder.end());
        return levelOrder;
    }
};

学习vector用法