图解LeetCode第 103 号问题：二叉树的锯齿形层次遍历

 1class Solution{
 2public:
 3    vector<vector<int>> zigzagLevelOrder(TreeNode* root){
 4        vector<vector<int>> res2D;
 5        if (!root) return res2D;
 6        queue<TreeNode*> q;
 7        q.push(root);
 8        int level=1;
 9        int count=1;
10        int countTmp=0;
11        while(!q.empty()){
12                countTmp=0;
13                vector<int> res1D;
14                while (count>0){
15                    res1D.push_back(q.front()->val);
16                    if (q.front()->left) {q.push(q.front()->left);countTmp++;}
17                    if (q.front()->right) {q.push(q.front()->right);countTmp++;}
18                    q.pop();
19                    count--;
20                }
21                if (level%2==0) reverse(res1D.begin(),res1D.end());   
22                count=countTmp;
23                res2D.push_back(res1D);
24                level++;               
25        }
26        return res2D;
27    }
28};