LeetCode - Binary Tree Level Order Traversal

Question

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]

]

Code

一个比较挫的版本，用上了队列。（C++ : 8ms）

/**
* 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>> result;
if(root == NULL) return result;

int len;
queue<TreeNode*> q;
q.push(root);
while(!q.empty()){
len = q.size();
vector<int> vet;
for(int i = 0; i < len; i++){
TreeNode *temp = q.front();
vet.push_back(temp->val);
if(temp->left != NULL) q.push(temp->left);
if(temp->right != NULL) q.push(temp->right);
q.pop();
}
result.push_back(vet);
}
return result;
}
};