【遍历二叉树】11把二叉树转换成前序遍历的链表【Flatten Binary Tree to Linked List】


本质上是二叉树的root->right->left遍历。

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

给定一个二叉树，就地的把他转换成一个链表。

例如：

给定

         1
        / \
       2   5
      / \   \
     3   4   6


转换后的树应该向这样子：


   1
    \
     2
      \
       3
        \
         4
          \
           5
            \
             6


提示：


如果你观察的足够仔细，你会发现，每个还在的右孩子指针指向了，这个节点在前序遍历中的后面的那个节点。


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


 Given a binary tree, flatten it to a linked list in-place.


For example,
Given


         1
        / \
       2   5
      / \   \
     3   4   6



The flattened tree should look like:


   1
    \
     2
      \
       3
        \
         4
          \
           5
            \
             6


Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.




++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


迭代版本：


test.cpp：










1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87



 


#include <iostream>
#include <cstdio>
#include <stack>
#include <vector>
#include "BinaryTree.h"

using namespace std;


/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
void flatten(TreeNode *root)
{
    if (root == NULL)
    {
        return ;
    }
    stack<TreeNode *> s;
    s.push(root);

    TreeNode *tmp;
    while (!s.empty())
    {
        tmp = s.top();
        s.pop();

        if (tmp->right)
        {
            s.push(tmp->right);
        }
        if (tmp->left)
        {
            s.push(tmp->left);
        }

        tmp->left = NULL;
        if (!s.empty())
        {
            tmp->right = s.top();
        }
    }
}



// 树中结点含有分叉，
//                  6
//              /       \
//             7         2
//           /   \
//          1     4
//               / \
//              3   5
int main()
{
    TreeNode *pNodeA1 = CreateBinaryTreeNode(6);
    TreeNode *pNodeA2 = CreateBinaryTreeNode(7);
    TreeNode *pNodeA3 = CreateBinaryTreeNode(2);
    TreeNode *pNodeA4 = CreateBinaryTreeNode(1);
    TreeNode *pNodeA5 = CreateBinaryTreeNode(4);
    TreeNode *pNodeA6 = CreateBinaryTreeNode(3);
    TreeNode *pNodeA7 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNodeA1, pNodeA2, pNodeA3);
    ConnectTreeNodes(pNodeA2, pNodeA4, pNodeA5);
    ConnectTreeNodes(pNodeA5, pNodeA6, pNodeA7);

    flatten(pNodeA1);

    TreeNode *trav = pNodeA1;
    while (trav != NULL)
    {
        cout << trav->val << " ";
        trav = trav->right;
    }
    cout << endl;

    DestroyTree(pNodeA1);
    return 0;
}















 


 


递归版本：


test.cpp：












1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86



 



#include <iostream>
#include <cstdio>
#include <stack>
#include <vector>
#include "BinaryTree.h"

using namespace std;


/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
void flatten(TreeNode *root)
{

    if(root == NULL)
    {
        return ;
    }
    if(root->left == NULL && root->right == NULL)
    {
        return ;
    }

    flatten(root->left);
    flatten(root->right);

    TreeNode *tmpright = root->right;
    /*因为是前序遍历*/
    root->right = root->left;
    root->left = NULL;
    TreeNode *tmp = root;
    while(tmp->right)
    {
        /*找到右子树的前序遍历的最后一个节点*/
        tmp = tmp->right;
    }
    tmp->right = tmpright;

    return ;
}



// 树中结点含有分叉，
//                  6
//              /       \
//             7         2
//           /   \
//          1     4
//               / \
//              3   5
int main()
{
    TreeNode *pNodeA1 = CreateBinaryTreeNode(6);
    TreeNode *pNodeA2 = CreateBinaryTreeNode(7);
    TreeNode *pNodeA3 = CreateBinaryTreeNode(2);
    TreeNode *pNodeA4 = CreateBinaryTreeNode(1);
    TreeNode *pNodeA5 = CreateBinaryTreeNode(4);
    TreeNode *pNodeA6 = CreateBinaryTreeNode(3);
    TreeNode *pNodeA7 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNodeA1, pNodeA2, pNodeA3);
    ConnectTreeNodes(pNodeA2, pNodeA4, pNodeA5);
    ConnectTreeNodes(pNodeA5, pNodeA6, pNodeA7);

    flatten(pNodeA1);

    TreeNode *trav = pNodeA1;
    while (trav != NULL)
    {
        cout << trav->val << " ";
        trav = trav->right;
    }
    cout << endl;

    DestroyTree(pNodeA1);
    return 0;
}




















结果输出：


6 7 1 4 3 5 2







BinaryTree.h:












1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21



 


#ifndef _BINARY_TREE_H_
#define _BINARY_TREE_H_

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};


TreeNode *CreateBinaryTreeNode(int value);
void ConnectTreeNodes(TreeNode *pParent,
                      TreeNode *pLeft, TreeNode *pRight);
void PrintTreeNode(TreeNode *pNode);
void PrintTree(TreeNode *pRoot);
void DestroyTree(TreeNode *pRoot);


#endif /*_BINARY_TREE_H_*/


















BinaryTree.cpp:










1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89



 


#include <iostream>
#include <cstdio>
#include "BinaryTree.h"

using namespace std;

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

//创建结点
TreeNode *CreateBinaryTreeNode(int value)
{
    TreeNode *pNode = new TreeNode(value);

    return pNode;
}

//连接结点
void ConnectTreeNodes(TreeNode *pParent, TreeNode *pLeft, TreeNode *pRight)
{
    if(pParent != NULL)
    {
        pParent->left = pLeft;
        pParent->right = pRight;
    }
}

//打印节点内容以及左右子结点内容
void PrintTreeNode(TreeNode *pNode)
{
    if(pNode != NULL)
    {
        printf("value of this node is: %d\n", pNode->val);

        if(pNode->left != NULL)
            printf("value of its left child is: %d.\n", pNode->left->val);
        else
            printf("left child is null.\n");

        if(pNode->right != NULL)
            printf("value of its right child is: %d.\n", pNode->right->val);
        else
            printf("right child is null.\n");
    }
    else
    {
        printf("this node is null.\n");
    }

    printf("\n");
}

//前序遍历递归方法打印结点内容
void PrintTree(TreeNode *pRoot)
{
    PrintTreeNode(pRoot);

    if(pRoot != NULL)
    {
        if(pRoot->left != NULL)
            PrintTree(pRoot->left);

        if(pRoot->right != NULL)
            PrintTree(pRoot->right);
    }
}

void DestroyTree(TreeNode *pRoot)
{
    if(pRoot != NULL)
    {
        TreeNode *pLeft = pRoot->left;
        TreeNode *pRight = pRoot->right;

        delete pRoot;
        pRoot = NULL;

        DestroyTree(pLeft);
        DestroyTree(pRight);
    }
}





















 







 






            

            
posted @ 
2014-04-08 16:49 
z陵 
阅读(278) 
评论(0) 
 
收藏 
举报