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| 1 | +#include <bits/stdc++.h> |
| 2 | +using namespace std; |
| 3 | + |
| 4 | +/* Link list node */ |
| 5 | +struct Node { |
| 6 | + int data; |
| 7 | + struct Node* next; |
| 8 | +}; |
| 9 | + |
| 10 | +/* Function to remove loop. */ |
| 11 | +void removeLoop(struct Node*, struct Node*); |
| 12 | + |
| 13 | +/* This function detects and removes loop in the list |
| 14 | +If loop was there in the list then it returns 1, |
| 15 | +otherwise returns 0 */ |
| 16 | +int detectAndRemoveLoop(struct Node* list) |
| 17 | +{ |
| 18 | + struct Node *slow_p = list, *fast_p = list; |
| 19 | + |
| 20 | + // Iterate and find if loop exists or not |
| 21 | + while (slow_p && fast_p && fast_p->next) { |
| 22 | + slow_p = slow_p->next; |
| 23 | + fast_p = fast_p->next->next; |
| 24 | + |
| 25 | + /* If slow_p and fast_p meet at some point then there |
| 26 | + is a loop */ |
| 27 | + if (slow_p == fast_p) { |
| 28 | + removeLoop(slow_p, list); |
| 29 | + |
| 30 | + /* Return 1 to indicate that loop is found */ |
| 31 | + return 1; |
| 32 | + } |
| 33 | + } |
| 34 | + |
| 35 | + /* Return 0 to indicate that there is no loop*/ |
| 36 | + return 0; |
| 37 | +} |
| 38 | + |
| 39 | +/* Function to remove loop. |
| 40 | +loop_node --> Pointer to one of the loop nodes |
| 41 | +head --> Pointer to the start node of the linked list */ |
| 42 | +void removeLoop(struct Node* loop_node, struct Node* head) |
| 43 | +{ |
| 44 | + struct Node* ptr1 = loop_node; |
| 45 | + struct Node* ptr2 = loop_node; |
| 46 | + |
| 47 | + // Count the number of nodes in loop |
| 48 | + unsigned int k = 1, i; |
| 49 | + while (ptr1->next != ptr2) { |
| 50 | + ptr1 = ptr1->next; |
| 51 | + k++; |
| 52 | + } |
| 53 | + |
| 54 | + // Fix one pointer to head |
| 55 | + ptr1 = head; |
| 56 | + |
| 57 | + // And the other pointer to k nodes after head |
| 58 | + ptr2 = head; |
| 59 | + for (i = 0; i < k; i++) |
| 60 | + ptr2 = ptr2->next; |
| 61 | + |
| 62 | + /* Move both pointers at the same pace, |
| 63 | + they will meet at loop starting node */ |
| 64 | + while (ptr2 != ptr1) { |
| 65 | + ptr1 = ptr1->next; |
| 66 | + ptr2 = ptr2->next; |
| 67 | + } |
| 68 | + |
| 69 | + // Get pointer to the last node |
| 70 | + while (ptr2->next != ptr1) |
| 71 | + ptr2 = ptr2->next; |
| 72 | + |
| 73 | + /* Set the next node of the loop ending node |
| 74 | + to fix the loop */ |
| 75 | + ptr2->next = NULL; |
| 76 | +} |
| 77 | + |
| 78 | +/* Function to print linked list */ |
| 79 | +void printList(struct Node* node) |
| 80 | +{ |
| 81 | + // Print the list after loop removal |
| 82 | + while (node != NULL) { |
| 83 | + cout << node->data << " "; |
| 84 | + node = node->next; |
| 85 | + } |
| 86 | +} |
| 87 | + |
| 88 | +struct Node* newNode(int key) |
| 89 | +{ |
| 90 | + struct Node* temp = new Node(); |
| 91 | + temp->data = key; |
| 92 | + temp->next = NULL; |
| 93 | + return temp; |
| 94 | +} |
| 95 | + |
| 96 | +// Driver Code |
| 97 | +int main() |
| 98 | +{ |
| 99 | + struct Node* head = newNode(50); |
| 100 | + head->next = newNode(20); |
| 101 | + head->next->next = newNode(15); |
| 102 | + head->next->next->next = newNode(4); |
| 103 | + head->next->next->next->next = newNode(10); |
| 104 | + |
| 105 | + /* Create a loop for testing */ |
| 106 | + head->next->next->next->next->next = head->next->next; |
| 107 | + |
| 108 | + detectAndRemoveLoop(head); |
| 109 | + |
| 110 | + cout << "Linked List after removing loop \n"; |
| 111 | + printList(head); |
| 112 | + return 0; |
| 113 | +} |
| 114 | + |
| 115 | +// This code has been contributed by Striver |
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