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]

思路：

層次遍歷，每一層選出當前層最大值。

vector<int> largestValues(TreeNode* root)
     {
         vector<int>result;
         if (root == NULL)return result;
         queue
 
<TreeNode*>que;
         que.push(root);
         int tempmax = INT_MIN;
         while (!que.empty())
         {
             int levelsize = que.size();
             TreeNode* temp;
             for (int i = 0; i < levelsize;i++)
             {
                 temp = que.front();
                 que.pop();
                 
 
if (temp->left != NULL)que.push(temp->left);
                 if (temp->right != NULL)que.push(temp->right);
                 tempmax = max(tempmax, temp->val);
             }
             result.push_back(tempmax);
             tempmax = INT_MIN;
         }
         return result;         
     }
 

[leetcode-515-Find Largest Value in Each Tree Row]