uva 10038 Jolly Jumpers

A sequence of n > 0 integers is called a jolly jumper if the absolute values of the difference between successive elements take on all the values 1 through n-1. For instance,   is a jolly jumper, because the absolutes differences are 3, 2, and 1 respectively. The definition implies that any sequence of a single integer is a jolly jumper. You are to write a program to determine whether or not each of a number of sequences is a jolly jumper. Each line of input contains an integer n <= 3000 followed by n integers representing the sequence. For each line of input, generate a line of output saying “Jolly” or “Not jolly”.

拙劣的代码

#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <iomanip>
#define max 3000+5

using namespace std;

int main(void)
{
    int n, a[max], i;

    while (cin >> n)
    {
        int x, y;
        cin >> x;
        for (i = 0; i < n - 1; i++)
        {
            cin >> y;
            a[i] = fabs((x) - (y));
            x = y;
        }
        sort(a, a + n - 1);
        int flag = 0;
        for (i = 0; i < n - 1; i++) 
        {
            if (a[i] != i + 1) 
            {
                cout << "Not jolly\n";
                flag = 1;
                break;
            }
        }
        if (!flag)
        {
            cout << "Jolly\n";
        }
    }

    return 0;
}