leetcode 日经贴，Cpp code -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) {
vector<vector<int> > ans;
queue<TreeNode *> q;
vector<int> level;
if (!root) {
return ans;
}
q.push(root);
q.push(NULL);
bool rev = false;
while (!q.empty()) {
TreeNode *r = q.front();
q.pop();
if (!r) {
if (rev) {
reverse(level.begin(), level.end());
}
rev = !rev;
ans.push_back(level);
level.clear();
if (!q.empty()) {
q.push(NULL);
}
} else {
level.push_back(r->val);
if (r->left) {
q.push(r->left);
}
if (r->right) {
q.push(r->right);
}
}
}
return ans;
}
};