二叉树的前中后序遍历非递归实现

1、前序遍历非递归实现

 1 class Solution {
 2 public:
 3     /*
 4      * @param root: A Tree
 5      * @return: Preorder in ArrayList which contains node values.
 6      */
 7     vector<int> preorderTraversal(TreeNode * root) {
 8         vector<int> res;
 9         if(root==NULL)return res;
10         std::stack<TreeNode *> sta;
11         sta.push(root);
12         while(sta.size())
13         {
14             TreeNode *p=sta.top();
15             sta.pop();
16             res.push_back(p->val);
17             if(p->right)sta.push(p->right);
18             if(p->left)sta.push(p->left);
19         }
20         return res;
21     }
22 };

2、中序遍历非递归实现

 1 class Solution {
 2 public:
 3     /*
 4      * @param root: A Tree
 5      * @return: Inorder in ArrayList which contains node values.
 6      */
 7     vector<int> inorderTraversal(TreeNode * root) {
 8        vector<int> res;
 9        if(root==NULL)return res;
10        std::stack<TreeNode *> sta;
11        TreeNode *p=root;
12        while(p || sta.size())
13        {
14            if(p){
15                sta.push(p);
16                p=p->left;
17            }else{
18                p=sta.top();
19                sta.pop();
20                res.push_back(p->val);
21                p=p->right;
22            }
23        }
24        return res;
25     }
26 };

3、后序遍历非递归实现

 1 class Solution {
 2 public:
 3     /*
 4      * @param root: A Tree
 5      * @return: Postorder in ArrayList which contains node values.
 6      */
 7     vector<int> postorderTraversal(TreeNode * root) {
 8         vector<int> res;
 9         if(root==NULL)return res;
10         std::stack<TreeNode *> sta;
11         std::stack<int> help;//增加一个辅助栈
12         sta.push(root);
13         while(sta.size())
14         {
15             TreeNode *p=sta.top();
16             sta.pop();
17             help.push(p->val);//先放入辅助栈
18             if(p->left)sta.push(p->left);
19             if(p->right)sta.push(p->right);
20         }
21         while(help.size())//再从辅助栈内倒出
22         {
23             int tmp=help.top();
24             help.pop();
25             res.push_back(tmp);
26         }
27         return res;
28     }
29 };

 

posted @ 2018-02-06 14:07  jeysin  阅读(213)  评论(0)  编辑  收藏  举报