Cycle in a linked list in C

Author: Deepali-Srivastava

linked-list/cycle-in-linked-list.c

@@ -0,0 +1,187 @@
+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+#include<stdio.h>
+#include<stdlib.h>
+
+struct node
+{
+	int info;
+	struct node *link;
+};
+
+struct node *createList(struct node *start);
+void displayList(struct node *start);
+struct node *insertInBeginning(struct node *start,int data);
+struct node *insertAtEnd(struct node *start,int data);
+void insertCycle(struct node *start, int x);
+struct node *findCycle(struct node *start);
+void removeCycle(struct node *start, struct node *pC);
+
+main()
+{
+	struct node *start=NULL;	
+	struct node *ptr;		
+	int x;
+
+	start=createList(start);
+	
+	if(start==NULL)
+		exit(1);
+  	
+	x=40;
+	insertCycle(start,x);
+	
+	ptr=findCycle(start);
+	
+	if(ptr==NULL)
+		printf("List is NULL terminated\n");
+	else
+	{
+		printf("Cycle found in the list\n");	
+		removeCycle(start, ptr);	
+		printf("Cycle Removed, now list is NULL terminated\n");
+	}
+	displayList(start);
+}/*End of main()*/
+
+
+/*Insert a cycle at node containing x*/
+void insertCycle(struct node *start, int x)
+{
+	struct node *p,*px=NULL, *prev, *ptr;		
+	
+	p=start;
+	while(p!=NULL)
+	{
+		if(p->info==x)
+			px=p;
+		prev=p;
+		p=p->link;
+	}
+	if(px!=NULL)
+		prev->link=px;
+}
+
+/*Returns NULL if the list is NULL terminated otherwise returns 
+pointer to node where both slow and fast pointers meet*/
+struct node *findCycle(struct node *start)
+{
+	struct node *slowP, *fastP;
+	
+	if(start->link==NULL) /*only one element*/
+		return NULL;
+
+	slowP=fastP=start;
+
+	while(fastP!=NULL && fastP->link!=NULL) 
+	{
+		slowP=slowP->link;
+		fastP=fastP->link->link;
+		if( slowP==fastP )
+			return slowP;
+	}
+	return NULL;
+}/*End of findCycle()*/
+
+void removeCycle(struct node *start, struct node *pC)
+{
+	struct node *p, *q;
+	int i, lenCycle, lenRemList, lengthList;
+		
+	printf("Node at which the cycle was detected is %d\n",pC->info);
+	
+	p=q=pC;	
+	lenCycle=0;
+	do
+	{
+		lenCycle++;
+		q=q->link;
+	}while(p!=q);
+	printf("Length of cycle is : %d\n",lenCycle);
+	
+	lenRemList=0;
+	p=start;
+	while(p!=q)
+	{
+		lenRemList++;
+		p=p->link;
+		q=q->link;
+	}
+	
+	printf("Number of nodes not included in the cycle are : %d\n",lenRemList);
+	
+	lengthList = lenCycle + lenRemList;
+	printf("Length of the list is : %d\n",lengthList);
+	
+	p=start;
+	for(i=1; i<=lengthList-1; i++)
+		p=p->link;
+	p->link=NULL;
+}
+
+struct node *createList(struct node *start)
+{
+	int i,n,data;
+	printf("Enter the number of nodes : ");
+	scanf("%d",&n);
+	start=NULL;
+	if(n==0)
+		return start;
+
+	printf("Enter the element to be inserted : ");
+	scanf("%d",&data);
+	start=insertInBeginning(start,data);
+
+	for(i=2;i<=n;i++)
+	{
+		printf("Enter the element to be inserted : ");
+		scanf("%d",&data);
+		start=insertAtEnd(start,data);	
+	}
+	return start;
+}/*End of createList()*/
+
+void displayList(struct node *start)
+{
+	struct node *p;
+	if(start==NULL)
+	{
+		printf("List is empty\n");
+		return;
+	}
+	p=start;
+	printf("List is :\n");
+	while(p!=NULL)
+	{
+		printf("%d ",p->info);
+		p=p->link;
+	}
+	printf("\n\n");
+}/*End of displayList() */
+
+struct node *insertInBeginning(struct node *start,int data)
+{
+	struct node *tmp;
+	tmp=(struct node *)malloc(sizeof(struct node));
+	tmp->info=data;
+	tmp->link=start;
+	start=tmp;
+	return start;
+}/*End of insertInBeginning()*/
+
+struct node *insertAtEnd(struct node *start,int data)
+{
+	struct node *p,*tmp;
+	tmp=(struct node *)malloc(sizeof(struct node));
+	tmp->info=data;
+	p=start;
+	while(p->link!=NULL)
+		p=p->link;
+	p->link=tmp;
+	tmp->link=NULL;
+	return start;
+}/*End of addAtEnd()*/
+