• 《Cracking the Coding Interview》——第17章:普通题——题目13


    2014-04-29 00:15

    题目:将二叉搜索树展开成一个双向链表,要求这个链表仍是有序的,而且不能另外分配对象,就地完成。

    解法:Leetcode上也有,递归解法。

    代码:

     1 // 17.13 Flatten a binary search tree into a doubly linked list by inorder traversal order.
     2 // Use postorder traversal to do the flattening job.
     3 #include <cstdio>
     4 using namespace std;
     5 
     6 struct TreeNode {
     7     int val;
     8     TreeNode *left;
     9     TreeNode *right;
    10     TreeNode(int _val = 0): val(_val), left(nullptr), right(nullptr) {};
    11 };
    12 
    13 void flatten(TreeNode *&root, TreeNode *&left_most, TreeNode *&right_most)
    14 {
    15     if (root == nullptr) {
    16         left_most = right_most = nullptr;
    17         return;
    18     }
    19     
    20     TreeNode *ll, *lr, *rl, *rr;
    21     if (root->left != nullptr) {
    22         flatten(root->left, ll, lr);
    23         root->left = lr;
    24         lr->right = root;
    25     } else {
    26         ll = lr = root;
    27     }
    28     
    29     if (root->right != nullptr) {
    30         flatten(root->right, rl, rr);
    31         root->right = rl;
    32         rl->left = root;
    33     } else {
    34         rl = rr = root;
    35     }
    36     
    37     left_most = ll;
    38     right_most = rr;
    39 }
    40 
    41 void constructBinaryTree(TreeNode *&root)
    42 {
    43     int val;
    44     
    45     if (scanf("%d", &val) != 1) {
    46         root = nullptr;
    47     } else if (val == 0) {
    48         root = nullptr;
    49     } else {
    50         root = new TreeNode(val);
    51         constructBinaryTree(root->left);
    52         constructBinaryTree(root->right);
    53     }
    54 }
    55 
    56 void deleteList(TreeNode *&head)
    57 {
    58     TreeNode *ptr;
    59     
    60     while (head != nullptr) {
    61         ptr = head;
    62         head = head->right;
    63         delete ptr;
    64     }
    65 }
    66 
    67 int main()
    68 {
    69     TreeNode *root;
    70     TreeNode *left_most, *right_most;
    71     TreeNode *head;
    72     TreeNode *ptr;
    73     
    74     while (true) {
    75         constructBinaryTree(root);
    76         if (root == nullptr) {
    77             break;
    78         }
    79         flatten(root, left_most, right_most);
    80         head = left_most;
    81         for (ptr = head; ptr != nullptr; ptr = ptr->right) {
    82             printf("%d ", ptr->val);
    83         }
    84         putchar('
    ');
    85         deleteList(head);
    86     }
    87     
    88     return 0;
    89 }
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  • 原文地址:https://www.cnblogs.com/zhuli19901106/p/3698317.html
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