1 文本格式

// CPP program to implement Brent's cycle  
// detection algorithm to detect cycle in 
// a linked list. 
#include <stdio.h> 
#include <stdlib.h> 

/* Link list node */
struct Node { 
    int data; 
    struct Node* next; 
}; 

/* This function detects loop in the list 
If loop was there in the list then it returns, 
the first node of loop otherwise returns NULL */
struct Node* detectCycle(struct Node* head) 
{ 
    // if head is null then no loop 
    if (head == NULL)  
        return NULL;     

    struct Node* first_pointer = head; 
    struct Node* second_pointer = head->next; 
    int power = 1; 
    int length = 1; 

    // This loop runs till we find the loop. 
    // If there is no loop then second_pointer 
    // ends at NULL . 
    while (second_pointer != NULL &&  
           second_pointer != first_pointer) { 

        // condition after which we will 
        // update the power and length as 
        // smallest power of two gives the 
        // start of cycle. 
        if (length == power) { 

            // updating the power. 
            power *= 2; 

            // updating the length 
            length = 0; 

            first_pointer = second_pointer; 
        } 

        second_pointer = second_pointer->next; 
        ++length; 
    } 

    // if it is null then no loop 
    if (second_pointer == NULL)  
        return NULL;     

    // Otherwise length stores actual length  
    // of loop. 
    // If needed, we can also print length of 
    // loop. 
    // printf("Length of loop is %d\n", length); 

    // Now set first_pointer to the beginning 
    // and second_pointer to beginning plus 
    // cycle length which is length. 
    first_pointer = second_pointer = head; 
    while (length > 0) { 
        second_pointer = second_pointer->next; 
        --length; 
    } 

    // Now move both pointers at same speed so 
    // that they meet at the beginning of loop. 
    while (second_pointer != first_pointer) { 
        second_pointer = second_pointer->next; 
        first_pointer = first_pointer->next; 
    } 

    // If needed, we can also print length of 
    // loop. 
    // printf("Length of loop is %d", length); 

    return first_pointer; 
} 

struct Node* newNode(int key) 
{ 
    struct Node* temp =  
      (struct Node*)malloc(sizeof(struct Node)); 
    temp->data = key; 
    temp->next = NULL; 
    return temp; 
} 

// Driver program to test above function 
int main() 
{ 
    struct Node* head = newNode(50); 
    head->next = newNode(20); 
    head->next->next = newNode(15); 
    head->next->next->next = newNode(4); 
    head->next->next->next->next = newNode(10); 

    // Create a loop for testing  
    head->next->next->next->next->next =  
                              head->next->next; 

    Node *res = detectCycle(head); 
    if (res == NULL) 
        printf("No loop"); 
    else
        printf("Loop is present at %d", res->data); 
    return 0; 
} 

2 代码格式

// CPP program to implement Brent's cycle  
// detection algorithm to detect cycle in 
// a linked list. 
#include <stdio.h> 
#include <stdlib.h> /* Link list node */
struct Node { int data; struct Node* next; 
}; /* This function detects loop in the list 
If loop was there in the list then it returns, 
the first node of loop otherwise returns NULL */
struct Node* detectCycle(struct Node* head) 
{ // if head is null then no loop if (head == NULL)  return NULL;     struct Node* first_pointer = head; struct Node* second_pointer = head->next; int power = 1; int length = 1; // This loop runs till we find the loop. // If there is no loop then second_pointer // ends at NULL . while (second_pointer != NULL &&  second_pointer != first_pointer) { // condition after which we will // update the power and length as // smallest power of two gives the // start of cycle. if (length == power) { // updating the power. power *= 2; // updating the length length = 0; first_pointer = second_pointer; } second_pointer = second_pointer->next; ++length; } // if it is null then no loop if (second_pointer == NULL)  return NULL;     // Otherwise length stores actual length  // of loop. // If needed, we can also print length of // loop. // printf("Length of loop is %d\n", length); // Now set first_pointer to the beginning // and second_pointer to beginning plus // cycle length which is length. first_pointer = second_pointer = head; while (length > 0) { second_pointer = second_pointer->next; --length; } // Now move both pointers at same speed so // that they meet at the beginning of loop. while (second_pointer != first_pointer) { second_pointer = second_pointer->next; first_pointer = first_pointer->next; } // If needed, we can also print length of // loop. // printf("Length of loop is %d", length); return first_pointer; 
} struct Node* newNode(int key) 
{ struct Node* temp =  (struct Node*)malloc(sizeof(struct Node)); temp->data = key; temp->next = NULL; return temp; 
} // Driver program to test above function 
int main() 
{ struct Node* head = newNode(50); head->next = newNode(20); head->next->next = newNode(15); head->next->next->next = newNode(4); head->next->next->next->next = newNode(10); // Create a loop for testing  head->next->next->next->next->next =  head->next->next; Node *res = detectCycle(head); if (res == NULL) printf("No loop"); elseprintf("Loop is present at %d", res->data); return 0; 
}