*(leetcode) Binary Tree Level Order Traversal (tree)

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,#,#,15,7}

,

3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

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

confused what

"{1,#,2,3}"

means? >
read more on how binary tree is serialized on OJ.

/**
 * Definition for binary tree
 * 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> > ans;
        if(NULL==root)   return ans;
        int level=1, nextLevel=0;
        queue<TreeNode *> q;
        vector<int> v;
        v.push_back(root->val);
        ans.push_back(v);
        TreeNode *tmp;
        q.push(root);
        while(!q.empty()){
            vector<int> v;
            nextLevel=0;
            while(level>0){
                tmp = q.front();
                q.pop();
                level--;
                if(tmp->left!=NULL){
                    q.push(tmp->left);
                    v.push_back(tmp->left->val);
                    nextLevel++;
                }
                if(tmp->right!=NULL){
                    q.push(tmp->right);
                    v.push_back(tmp->right->val);
                    nextLevel++;
                }
            }
            if(nextLevel==0)
                return ans;
            ans.push_back(v);
            level=nextLevel;
        }
    }
};