[LeetCode] Binary Tree Level Order Traversal

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]
]

/**
* 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) {
// Start typing your C/C++ solution below
// DO NOT write int main() function

vector<int> level;
vector<vector<int> > ans;
if ( !root )
return ans;

queue<TreeNode* > Q;
Q.push(root);
int lsum=1;

while(lsum>0)
{
int next=0;
level.clear();
while(lsum--)
{
TreeNode* tmp=Q.front();
Q.pop();
level.push_back(tmp->val);
if ( tmp->left )
{
Q.push(tmp->left);
next++;
}
if ( tmp->right)
{
Q.push(tmp->right);
next++;
}
}
ans.push_back(level);
lsum=next;
}
return ans;
}
};