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,#,#,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>> res;         if(!root) return res;         queue<TreeNode *> que;         que.push(root);         TreeNode *first=root->left ? root->left:root->right;         TreeNode *p=NULL;         vector<int> v;         while(!que.empty()){             p=que.front();             que.pop();             if(p==first){                 res.push_back(v);                 v.clear();                 first = NULL;             }             v.push_back(p->val);             if(!first && p->left){                 first = p->left;             }             if(!first && p->right){                 first = p->right;             }             if(p->left) que.push(p->left);             if(p->right) que.push(p->right);         }         if(v.size()) res.push_back(v);         return res;    }};