之字形打印二叉树

 1 /*
 2 struct TreeNode {
 3     int val;
 4     struct TreeNode *left;
 5     struct TreeNode *right;
 6     TreeNode(int x) :
 7             val(x), left(NULL), right(NULL) {
 8     }
 9 };
10 */
11 class Solution {
12 public:
13     vector<vector<int> > Print(TreeNode* pRoot) {
14         vector<vector<int> > result;
15         vector<int> vec_tmp;
16         //边界
17         if(pRoot==nullptr) return result;
18         //辅助容器:两个栈
19         //声明变量时后面加个[]表示是数组
20         stack<TreeNode*> s[2];//s[0]是奇数层，s[1]是偶数层；栈数组
21         int now=0;
22         int next=1;
23         TreeNode* temp=pRoot;
24         //根节点入栈
25         s[now].push(temp);
26         //遍历两个栈，当两个栈都为空时，跳出循环
27         while(!s[now].empty() || !s[next].empty()){
28             //存储遍历结果
29             temp = s[now].top();
30             vec_tmp.push_back(temp->val);
31             s[now].pop();
32             //当前层是奇数层还是偶数层
33             if(now==0){
34                 if(temp->left) s[next].push(temp->left);
35                 if(temp->right) s[next].push(temp->right);
36             }
37             else{
38                 if(temp->right) s[next].push(temp->right);
39                 if(temp->left) s[next].push(temp->left);
40             }
41             //当前层为空时，打印下一层
42             if(s[now].empty()){
43                 result.push_back(vec_tmp);
44                 vec_tmp.clear();
45                 now = 1-now;
46                 next=1-next;
47             }
48         }
49         return result;
50     }
51 };