102. Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

/**
 * 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> levelOrder(TreeNode* root) { 
		vector> ans; 
		if (root == NULL) return  ans; 
		vector level_Number; 
		queue T; 
		T.push(root); 
		int levelPostion=0; 
		int levelNow = 1;
		int nextLevel=0;

		while (!T.empty())
		{
			TreeNode * temp = T.front();		
			T.pop(); 



			if (temp->left != NULL)
			{
				T.push(temp->left); 
				nextLevel++;
			}

			if (temp->right != NULL)
			{
				T.push(temp->right); 
				nextLevel++;
			}


			levelPostion++;
			level_Number.push_back(temp->val);
			if (levelPostion == levelNow)
			{
				ans.push_back(level_Number);
				level_Number.clear();
				levelPostion = 0;
				levelNow = nextLevel;
				nextLevel = 0;
			}

		}

        return ans;
	}
};