FindNthElement.cpp

#include <bits/stdc++.h>
using namespace std;

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

node* init(int a[], int n) {
	node *head, *p;
	for (int i = 0; i < n; ++i) {
		node *nd = new node();
		nd->data = a[i];
		if (i == 0) {
			head = p = nd;
			continue;
		}
		p->next = nd;
		p = nd;
	}
	return head;
}

node* findNthToLast(node *head, int n) {
	if (head == NULL || n < 1) return NULL;
	node *p = head, *q = head;
	while (n > 0 && q) {
		q = q->next;
		--n;
	}
	if (n > 0) return NULL;
	while (q) {
		p = p->next;
		q = q->next;
	}
	return p;
}
node *pp;
int nn;
void findNthToLast1(node *head) {
	if (head == NULL) return;
	findNthToLast1(head->next);
	if (nn == 1) pp = head;
	--nn;
}
int main() {
	int n = 10;
	int a[] = {
		1, 2, 3, 4, 35, 6, 7, 8, 9, 10
	};
	node *head = init(a, n);
	node *p = findNthToLast(head, 6);
	if (p) cout << p->data << endl;
	else cout << "the length of link is not long enough" << endl;
	nn = 6;
	findNthToLast1(head);
	if (pp) cout << pp->data << endl;
	return 0;
}