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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. struct node
  5. {
  6.     int value = 0;
  7.     node *next = nullptr;
  8. };
  9.  
  10. node* get_node_at(node *head, int index, node **previous = nullptr)
  11. {
  12.     if (previous) *previous = nullptr;
  13.  
  14.     if ((!head) || (index < 0)) return nullptr;
  15.  
  16.     node *temp = head;
  17.     while (index > 0)
  18.     {
  19.         if (!temp) return nullptr;
  20.         if (previous) *previous = temp;
  21.         temp = temp->next;
  22.         --index;
  23.     }
  24.  
  25.     return temp;
  26. }
  27.  
  28. void swap_nodes(node *&head, int i, int j)
  29. {
  30.     if ((!head) || (i == j)) return;
  31.  
  32.     node *previous_i, *previous_j;
  33.     node* temp_i = get_node_at(head, i, &previous_i);
  34.     node* temp_j = get_node_at(head, j, &previous_j);
  35.  
  36.     if (!temp_i || !temp_j)
  37.         return;
  38.  
  39.     if (previous_i)
  40.         previous_i->next = temp_j;
  41.  
  42.     if (previous_j)
  43.         previous_j->next = temp_i;
  44.  
  45.     node *temp = temp_i->next;
  46.     temp_i->next = temp_j->next;
  47.     temp_j->next = temp;
  48.  
  49.    if (temp_i == head)
  50.        head = temp_j;
  51.    else if (temp_j == head)
  52.        head = temp_i;
  53. }
  54.  
  55. int main()
  56. {
  57.     node *head = nullptr;
  58.     node **ptr = &head;
  59.  
  60.     for (int i = 1; i <= 5; ++i)
  61.     {
  62.         *ptr = new node;
  63.         (*ptr)->value = i;
  64.         ptr = &((*ptr)->next);
  65.     }
  66.  
  67.     cout << "Before: ";
  68.     for(node *temp = head; temp != nullptr; temp = temp->next)
  69.         cout << temp->value << " ";
  70.     cout << endl;
  71.  
  72.     swap_nodes(head, 0, 4);
  73.     swap_nodes(head, 1, 3);
  74.  
  75.     cout << "After: ";
  76.     for(node *temp = head; temp != nullptr; temp = temp->next)
  77.         cout << temp->value << " ";
  78.     cout << endl;
  79.  
  80.     for(node *temp = head; temp != nullptr;)
  81.     {
  82.         node *n = temp;
  83.         temp = temp->next;
  84.         delete n;
  85.     }
  86.  
  87.     return 0;
  88. }
Success #stdin #stdout 0s 4392KB
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stdin
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Standard input is empty
stdout
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Before: 1 2 3 4 5 
After: 5 4 3 2 1
https://ideone.com/CAxCc7
language:
C++ (gcc 8.3)
created:
7 years ago
visibility:
public

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