POJ_2381_Random_Gap

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <stack>
#include <bitset>
#include <queue>
#include <list>
#include <vector>
#include <map>
#include <set>
#include <iterator>
#include <sstream>
#include <stdlib.h>
#include <cmath>
#define FOR(i,A) for(typeof (A).begin() i = (A).begin() ; i != (A).end() ; i++)
#define debug( x ) cout << #x << " = " << x << endl
#define clr(v,x) memset( v, x , sizeof v )
#define all(x) (x).begin() , (x).end()
#define rall(x) (x).rbegin() , (x).rend()
#define TAM 110

using namespace std;

typedef pair<int,int> ii ;
typedef long long ll ;
typedef long double ld ;
typedef pair<int,ii> pii ;
int seq[16000005];
int main() {
    long a,ro,c,m;
    scanf("%ld %ld %ld %ld",&a,&c,&m,&ro);
        a%=m;
        c%=m;
        seq[ro]=1;
        while(true)
        {
        ro=(ro%m*a%m+c)%m;  /*sequence*/
        if(seq[ro]==1 )break;/*fin*/
        seq[ro]=1;
        }
        long aux=m;long maxi=0;
         for(int i=0;i<m;i++){
        if(seq[i])
        {
            if(maxi<i-aux) maxi=i-aux;
            aux=i;/*guardo indice*/
        }
         }
        printf("%ld\n",maxi);



    return 0;
}