LeetCode Binary Tree Zigzag Level Order Traversal

题目：

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]
]

/**
* 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) {
vector<vector<int>> ans;
if(root == NULL)
return ans;
deque<int> level;
bool flag = 1;
vector<TreeNode*> cur;
cur.push_back(root);
vector<TreeNode*> next;
while(!cur.empty()) {
level.clear();
next.clear();
int bg = 0, ed = cur.size();
while(bg != ed) {
TreeNode *tmp = cur[bg];
if(flag)
level.push_back(tmp->val);
else
level.push_front(tmp->val);
if(tmp->left != NULL)
next.push_back(tmp->left);
if(tmp->right != NULL)
next.push_back(tmp->right);
bg++;
}
flag = 1-flag;
ans.push_back(vector<int>(level.begin(), level.end()));
cur = next;
}
return ans;
}
};

代码参考：/article/8613122.html