Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:

Given binary tree

{3,9,20,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its zigzag level order traversal as:

[
[3],
[20,9],
[15,7]
]

confused what

"{1,#,2,3}"

means? >
read more on how binary tree is serialized on OJ.

和binary tree level order traversal一样，最后加了个zigzag就奇数行倒置

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void levelTravel(vector<vector<int> >& result,int l, TreeNode*p){
if(!p) return;
if(result.size()>l) result[l].push_back(p->val);
else{
vector<int> v;
v.push_back(p->val);
result.push_back(v);
}
levelTravel(result,l+1,p->left);
levelTravel(result,l+1,p->right);
}
vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
vector<vector<int>> result;
levelTravel(result,0,root);
for(int i=0;i<result.size();i++)
if(i&1) reverse(result[i].begin(),result[i].end());
return result;
}
};