You need to find the largest value in each row of a binary tree.

Example:

Input: 

          1
         /         3   2
       / \   \  
      5   3   9 

Output: [1, 3, 9]

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/

//方法一：叠代，自己寫的
class Solution {
public:
vector<int> largestValues(TreeNode* root) {
queue<TreeNode*>q;
vector<int>ret;
if(root==NULL)
return ret;
int maxi=INT_MIN;
q.push(root);
q.push(nullptr);
while(!q.empty())
{
TreeNode*t=q.front();
q.pop();
if(t==nullptr)
{
ret.push_back(maxi);
maxi=INT_MIN;
if(!q.empty())
q.push(nullptr);
}
else
{
maxi=max(maxi,t->val);
if(t->left)
q.push(t->left);
if(t->right)
q.push(t->right);
}
}
return ret;
}
};

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/

//方法二：遞歸，看的別人的解法
class Solution {
public:
vector<int>ret;
void helper(TreeNode*root,int cl)
{
if(root==NULL)
return;
if(ret.size()<cl+1)
ret.push_back(root->val);
else
{
if(ret[cl]<root->val)
ret[cl]=root->val;
}
helper(root->left,cl+1);
helper(root->right,cl+1);

}
vector<int> largestValues(TreeNode* root) {
if(root==NULL)
return ret;
helper(root,0);
return ret;
}
};

515. Find Largest Value in Each Tree Row