[Leetcode]Binary Tree Zigzag Level Order Traversal

/**
* 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> > zigzagLevelOrder(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<vector<int> > ret;
if(root == NULL) return ret;
vector<int> ans;
queue<pair<TreeNode*, int> > q;
q.push(make_pair(root, 0));
int curLevel = 0;
while(!q.empty())
{
TreeNode *node = q.front().first;
int level = q.front().second;
q.pop();
if(level != curLevel)
{
curLevel++;
ret.push_back(ans);
ans.clear();
}
ans.push_back(node->val);
if(node->left != NULL)
q.push(make_pair(node->left, level+1));
if(node->right != NULL)
q.push(make_pair(node->right, level+1));
}
ret.push_back(ans);
for(int i = 0; i < ret.size(); ++i)
if(i % 2)
reverse(ret[i].begin(), ret[i].end());
return ret;
}
};