Binary Tree Zigzag Level Order Traversal 二叉树锯齿形层次遍历

class Solution {
public:
vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
vector<vector<int> > res;
if (root == NULL)
return res;
queue<TreeNode *> que;
que.push(root);
vector<int> row;
bool flag = true;
while (!que.empty())
{
row.clear();
flag = !flag;
int size = que.size();
while (size)
{
TreeNode *node = que.front();
que.pop();
if (flag)
row.insert(row.begin(), node->val);
else
row.push_back(node->val);
if (node->left) que.push(node->left);
if (node->right) que.push(node->right);
--size;
}
res.push_back(row);
}
return res;
}
};