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<vector<int>> levelOrderBottom(TreeNode* root) 
    {
        vector<vector<int>> ret;
        
        if(root==NULL) return ret;
        queue<TreeNode*> q;
        q.push(root);

        while(!q.empty())
        {
            vector<int> v;
            int size=q.size();

            for(int i=0;i<size;i++)
            {
                TreeNode* node=q.front();
                q.pop();
                v.push_back(node->val);

                if(node->left!=NULL) q.push(node->left);
                if(node->right!=NULL) q.push(node->right);
            }

            ret.push_back(v);
        }

        reverse(ret.begin(),ret.end());//直接调用STL里面的库函数

        return ret;
    }
};