分析

理论参考 辗转相减法

见注释

#include<iostream>
#include<cstring>
#include<algorithm>
#include<set>

using namespace std;

#define ffor(i,s,e) for(int i=s;i<e;i++)
#define out(x) cout<<x<<" "
#define nl cout<<endl
#define read(x) scanf("%lld",&x)

typedef long long LL;
const int N=105;

//data
int n;
LL a[N];
LL up[N],down[N];

//fun
void init(){
    read(n);
    set<LL> has;

    int idx=0;
    ffor(i,0,n){
        LL t;
        read(t);
        if(!has.count(t)){
            has.insert(t);
            a[idx]=t;
            ++idx;
        }
    }

    n=idx;
    sort(a,a+idx);
}

LL  gcd(LL  a,LL b) {
    if(a==0) return b;
    if(b==0) return a;
    while(b^=a^=b^=a%=b);//三异或加一余
    return a;
}

LL gcd_sub(LL a,LL b)//辗转相减
{
    if(b>a) swap(a,b);
    if(b==1) return a;
    return gcd_sub(b,a/b);
}


void updown(){
    ffor(i,1,n){
        LL x=a[i-1],y=a[i];
        LL _gcd=gcd(x,y);

        up[i]=y/_gcd;
        down[i]=x/_gcd;
    }

}

void getAns(){
    int a=up[1],b=down[1];
    ffor(i,2,n){
        a=gcd_sub(up[i],a);
        b=gcd_sub(down[i],b);
    }
    cout<<a<<"/"<<b<<endl;
}

//Ac flow
void Ac(){
    init();
    updown();
    getAns();
}

int main(){


    Ac();
    return 0;
}

gcd的几种写法

//way1
#include <algorithm>
int gcd(int a,int b) {
    return __gcd(a,b);
}


//way2

int gcd(int a,int b) {
    return b>0 ? gcd(b,a%b):a;
}

//way3
inline int gcd(int a,int b) {
    int r;
    while(b>0) {
        r=a%b;
        a=b;
        b=r;
    }
    return a;
}