findNthNodeIter.c

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
  int data;
  struct Node * next;
} Node;

Node * createNode(int val){
  Node * temp = (Node *)malloc(sizeof(Node));
  if(temp){
    temp->data = val;
    temp->next = NULL;
  }
  return temp;
}
/* This function inserts node at the head of linked list */
void push(Node **headRef, int data){
	Node * newNode  = createNode(data);
	newNode->next = *headRef;
	*headRef  = newNode;
}
void printList(Node *head){
	while(head){
		printf("%d->", head->data);
		head = head->next;
	}
	printf("Null");
}

Node * findNthNode(Node *head, int n){
	if(!head) return NULL;
	
	int counter = 0;
	Node *first = head;
	Node *second = head;
	
	//If n is negative
	if(n<0) {
		printf("\n Wrong input: Negative n");
	}
	
	while(first && counter < n){
		first  = first->next;
		counter++;
	}
	if(!first) {
		printf("\n Not enough nodes in list to find nth node");
		return NULL;
	}
	
	while(first){
		first = first->next;
		second = second->next;
	}
	return second;
}

int main(void) {
	
	Node *head = NULL;
	Node *nthNode = NULL;
	push(&head, 3);
	push(&head, 4);
	Node * nodeToDelete = head;
	push(&head, 5);
	push(&head, 6);
	push(&head, 7);
	push(&head, 8);
	push(&head, 9);
	printf("\nOriginal list :");
	printList(head);
	nthNode = findNthNode(head,3);
    printf("\nNth node from end : %d",  nthNode ? nthNode->data : 0);
	return 0;
}