LeetCode#103. 二叉树的锯齿形层次遍历

题目链接：https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/description/

class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) 
    {
        //与层次遍历思路相同，只需设置深度的奇偶标志，二叉树深度为偶数时反转
        vector<vector<int>> ret;
        vector<int> level;
        int count = 0;

        if(root == NULL)
            return ret;

        queue q;
        q.push(root);
        q.push(NULL);

        while(!q.empty())
        {
            TreeNode* temp = q.front();
            q.pop();
            if(temp != NULL)
            {
                level.push_back(temp->val);
                if(temp->left)
                    q.push(temp->left);
                if(temp->right)
                    q.push(temp->right); 
            }
            else
            {
                count += 1;
                if(count % 2 != 0)
                    ret.push_back(level);
                else
                {
                    reverse(level.begin(), level.end());
                    ret.push_back(level);
                }
                if(!q.empty())
                {
                    level.clear();
                    q.push(NULL);
                }
            }
        }
        return ret;
    }
};