Uniform Generator

Computer simulations often require random numbers. One way to generate pseudo-random numbers is via a function of the form 

seed(x+1) = [seed(x) + STEP] % MOD 

where ‘%‘ is the modulus operator. 

Such a function will generate pseudo-random numbers (seed) between 0 and MOD-1. One problem with functions of this form is that they will always generate the same pattern over and over. In order to minimize this effect, selecting the STEP and MOD values carefully can result in a uniform distribution of all values between (and including) 0 and MOD-1. 

For example, if STEP = 3 and MOD = 5, the function will generate the series of pseudo-random numbers 0, 3, 1, 4, 2 in a repeating cycle. In this example, all of the numbers between and including 0 and MOD-1 will be generated every MOD iterations of the function. Note that by the nature of the function to generate the same seed(x+1) every time seed(x) occurs means that if a function will generate all the numbers between 0 and MOD-1, it will generate pseudo-random numbers uniformly with every MOD iterations. 

If STEP = 15 and MOD = 20, the function generates the series 0, 15, 10, 5 (or any other repeating series if the initial seed is other than 0). This is a poor selection of STEP and MOD because no initial seed will generate all of the numbers from 0 and MOD-1. 

Your program will determine if choices of STEP and MOD will generate a uniform distribution of pseudo-random numbers. 

3 5
15 20
63923 99999

         3         5    Good Choice

        15        20    Bad Choice

     63923     99999    Good Choice





思路  ： 水了两晚上的题，差点淹死.......这个题有两种做法，首先就是普通做法，其次就是求两个数最大公约数是不是一；

第一种方法：

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int s,mod,i;
    while(~scanf("%d%d",&s,&mod))
    {
        int a[100001] = {0},seed=0;
        while(!a[seed]){
            a[seed] = 1;
            seed = (seed+s)%mod;
        }
        for(i=0;i<mod;i++){
           if(a[i] == 0){
              printf("%10d%10d    Bad Choice\n\n",s,mod);break;
           }
        }
        if(i==mod){
        	printf("%10d%10d    Good Choice\n\n",s,mod);
        }
    }
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int step,mod1,t;
    while(scanf("%d%d",&step,&mod1)==2)
    {
        printf("%10d%10d",step,mod1);
        while(mod1)
        {
            t = step%mod1;
            step = mod1;
            mod1 = t;
        }
        printf("    %s\n\n",step == 1? "Good Choice":"Bad Choice");
    }
    return 0;
}