Binary Tree Level Order Traversal

法一：

vector<vector<int>> levelOrder(TreeNode* root) 
    {
        vector<vector<int>> res;
        vector<int> tem;      //临时vector
        list<TreeNode*> l1;   //存储节点list
        list<int> l2;         //存储对应节点深度信息list     
        if(!root)
            return res;
        l1.push_back(root);   
        l2.push_back(1);
        int cur = 1;          //当前深度
        while(!l1.empty())    //list为空跳出循环
        {                               
            if(l1.front()->left)               
            {
                l1.push_back(l1.front()->left);//有左孩子加l1中
                l2.push_back(l2.front()+1); //对应的深度+1
            }
            if(l1.front()->right)
            {
                l1.push_back(l1.front()->right);//有右孩子加l1中
                l2.push_back(l2.front()+1);//对应的深度+1
            }
            if(cur==l2.front())
                tem.push_back(l1.front()->val);  //深度相同，就加到tem中
            else
            {
                res.push_back(tem);              //深度不同，把之前的tem添加到res中
                tem.clear(); 
                cur++;                           //当前深度+1
                tem.push_back(l1.front()->val);  
            }
            l1.erase(l1.begin());                //每次循环移除l1头节点
            l2.erase(l2.begin());                //每次循环移除l2头节点
            
            
        }
        res.push_back(tem);
        return res;
    }</span>

法二：

private:
    vector<vector<int>> res;
public:

    void buildVector(TreeNode * root,int depth)
    {
        if(!root)
            return;
        if(res.size()==depth)
            res.push_back(vector<int>());
        res[depth].push_back(root->val);
        buildVector(root->left,depth+1);
        buildVector(root->right,depth+1);
    }

    
    vector<vector<int>> levelOrder(TreeNode* root) 
    {
        buildVector(root,0);
        return res;

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