Leetcode 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,null,null,15,7],

    3   / \  9  20    /  \   15   7

return its zigzag level order traversal as:

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

---

代码如下：

/** * Definition for a binary tree node. * 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>> result;          if(root == NULL)              return result;                  int count = 0;          deque<TreeNode*> level;          level.push_back(root);          while(!level.empty())          {              int num = level.size();              vector<int> data(num);            for(int i=0;i<num;i++)              {                              if(level.front()->left != NULL)                      level.push_back(level.front()->left);                  if(level.front()->right != NULL)                      level.push_back(level.front()->right);                if(count %2 ==0)                    data[i] = level.front()->val;                else                    data[num-i-1] = level.front()->val;                level.pop_front();              }            count++;            result.push_back(data);          }          return result;      }};