LeetCode:102. 二叉树的层序遍历

/**
 * 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>> levelOrder(TreeNode* root) 
    {
        queue<TreeNode*> level;
        vector<vector<int>> res;
        vector<int> temp;
        if(root==NULL)
        {
            return res;
        }
        else
        {
            level.push(root);
            temp.push_back(root->val);
            res.push_back(temp);
        }
        int size=0;
        //从根节点开始不断地遍历
        while(!level.empty())
        {
            //保存当前队列中的元素，//每一次经过这里战中存储的就是一行的元素
            size=level.size();
            int i=0;
            temp.clear();//清空
            while(i<size)
            {
                if(level.front()->left!=NULL)
                {
                    temp.push_back(level.front()->left->val);
                    level.push(level.front()->left);
                }
                if(level.front()->right!=NULL)
                {
                    temp.push_back(level.front()->right->val);
                    level.push(level.front()->right);
                }
                level.pop();
                i++;
            }
            if(temp.size()!=0)
                res.push_back(temp);
        }
        return res;

    }

};