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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. struct ListNode {
  5.     int val;
  6.     ListNode *next;
  7.     ListNode() : val(0), next(nullptr) {}
  8.     ListNode(int x) : val(x), next(nullptr) {}
  9.     ListNode(int x, ListNode *next) : val(x), next(next) {}
  10. };
  11.  
  12. void printList(ListNode* head) {
  13.     while (head) {
  14.         cout << head->val << " ";
  15.         head = head->next;
  16.     }
  17.     cout << endl;
  18. }
  19.  
  20. class Solution {
  21. public:
  22.     ListNode* reverseBetween(ListNode* head, int left, int right) {
  23.         if (!head || left == right) return head;
  24.  
  25.         ListNode dummy(0);
  26.         dummy.next = head;
  27.         ListNode* prev = &dummy;
  28.  
  29.         for (int i = 0; i < left - 1; i++) {
  30.             prev = prev->next;
  31.         }
  32.  
  33.         ListNode* curr = prev->next;
  34.         ListNode* next = nullptr;
  35.  
  36.         cout << "Initial list before reversing: ";
  37.         printList(dummy.next);
  38.         // cout << "Current: " << curr->val << " Next: "<<next->val<<" Prev: "<<prev->val<<endl;
  39.  
  40.         for (int i = 0; i < right - left; i++) {
  41.             next = curr->next;
  42.             curr->next = next->next;
  43.             next->next = prev->next;
  44.             prev->next = next;
  45.  
  46.             cout << "After iteration " << i + 1 << ": ";
  47.             cout << "Current: " << curr->val << " Next: "<<next->val<<" Prev: "<<prev->val<<endl;
  48.             printList(dummy.next);
  49.         }
  50.  
  51.         return dummy.next;
  52.     }
  53. };
  54.  
  55.  
  56.  
  57. int main() {
  58.     ListNode* head = new ListNode(1);
  59.     head->next = new ListNode(2);
  60.     head->next->next = new ListNode(3);
  61.     head->next->next->next = new ListNode(4);
  62.     head->next->next->next->next = new ListNode(5);
  63.  
  64.     int left = 2, right = 4;
  65.     Solution sol;
  66.     head = sol.reverseBetween(head, left, right);
  67.  
  68.     cout << "Final reversed list: ";
  69.     printList(head);
  70.  
  71.     return 0;
  72. }
  73.  
Success #stdin #stdout 0.01s 5280KB
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stdin
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Standard input is empty
stdout
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Initial list before reversing: 1 2 3 4 5 
After iteration 1: Current: 2 Next: 3 Prev: 1
1 3 2 4 5 
After iteration 2: Current: 2 Next: 4 Prev: 1
1 4 3 2 5 
Final reversed list: 1 4 3 2 5
https://ideone.com/Y4KBj6
language:
C++ (gcc 8.3)
created:
12 days ago
visibility:
public

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