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

typedef struct _node {
    int element;
    struct _node *next;
} node;

typedef node *stack;

stack init ()
{
   return NULL;
}

int isempty ( stack S )
{
    return (S == NULL);
}

int top ( stack S )
{
    if (isempty(S)) {
        printf("Error: top in an empty stack\n");
        return -1;
    }
    return S -> element;
}

stack push ( stack S, int a )
{
    node *p;

    p = (node *)malloc(sizeof(node));
    p -> element = a;
    p -> next = S;
    return p;
}

stack pop ( stack S )
{
    node *p;

    if (isempty(S)) {
        printf("Error: pop in an empty stack\n");
        return S;
    }
    p = S;
    S = S -> next;
    free(p);
    return S;
}

int main ( )
{
    int A[100], n, NLV[100], t, i;
    stack S;
    srand((unsigned int)time(NULL));

    printf("n = "); scanf("%d", &n);
    for (i=0; i<n; ++i) A[i] = rand() % 100;
    for (i=0; i<n; ++i) printf("%d ", A[i]);
    printf("\n");

    S = init();
    for (i=0; i<n; ++i) NLV[i] = -1;
    for (i=0; i<n; ++i) {
        while (!isempty(S)) {
            t = top(S);
            if (A[i] > A[t]) {
                NLV[t] = i;
                S = pop(S);
            } else {
                break;
            }
        }
        S = push(S,i);
    }

    for (i=0; i<n; ++i)
        if (NLV[i] == -1)
            printf("NLV of A[%d] = %d is undefined\n", i, A[i]);
        else
            printf("NLV of A[%d] = %d is A[%d] = %d\n", i, A[i], NLV[i], A[NLV[i]]);

    exit(0);
}