[LeetCode 102] Binary Tree Level Order Traversal

https://leetcode.com/problems/binary-tree-level-order-traversal/

http://www.lintcode.com/zh-cn/problem/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 of TreeNode:

 * class TreeNode {

 * public:

 *     int val;

 *     TreeNode *left, *right;

 *     TreeNode(int val) {

 *         this->val = val;

 *         this->left = this->right = NULL;

 *     }

 * }

 */

 

 

class Solution {

    /**

     * @param root: The root of binary tree.

     * @return: Level order a list of lists of integer

     */

public:

    vector<vector<int>> levelOrder(TreeNode *root) {

        // write your code here

        vector<vector<int> > ret;

        queue<TreeNode *> q;

        

        if (root == NULL) {

            return ret;

        }

        

        q.push(root);

        q.push(NULL);

        

        while (!q.empty() && q.front() != NULL) {

            vector<int> subRet;

            

            while (true) {

                TreeNode *node = q.front();

                

                if (node == NULL) {

                    q.pop();

                    q.push(NULL);

                    break;

                }

                

                if (node->left) {

                    q.push(node->left);

                }

                

                if (node->right) {

                    q.push(node->right);

                }

                

                subRet.push_back(node->val);

                

                q.pop();

            }

            

            ret.push_back(subRet);

        }

        

        return ret;

    }



};