leetcode 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]]

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/** * 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) {        vector<vector<int>> res;queue<TreeNode*> q;TreeNode *temp=NULL;if(root == NULL) return res;q.push(root);q.push(NULL);vector<int> vec;while(!q.empty()) {temp = q.front();q.pop();if(temp!=NULL) {vec.push_back(temp->val);if(temp->left!=NULL)q.push(temp->left);if(temp->right!=NULL)q.push(temp->right);} else {q.push(NULL);res.push_back(vec);vec.clear();if(q.front()==NULL) break;}}return res;    }};