POJ 2891 Strange Way to Express Integers(中国剩余定理)

题目链接

虽然我不懂...

#include <cstdio>
#include <cstring>
#include <map>
#include <cmath>
using namespace std;
#define LL __int64
LL p[1001],o[1001];
LL x,y;
LL ext_eulid(LL a,LL b)
{
    LL t,d;
    if(b == 0)
    {
        x = 1;
        y = 0;
        return a;
    }
    d = ext_eulid(b,a%b);
    t = x;
    x = y;
    y = t - (a/b)*y;
    return d;
}
LL gcd(LL a,LL b)
{
    return b == 0?a:gcd(b,a%b);
}
int main()
{
    int i,n,z;
    LL p1,o1,d,c,mod;
    while(scanf("%d",&n)!=EOF)
    {
        for(i = 0;i < n;i ++)
        {
            scanf("%I64d%I64d",&p[i],&o[i]);
        }
        p1 = p[0];
        o1 = o[0];
        z = 1;
        for(i = 1;i < n&&z;i ++)
        {
            d = ext_eulid(p1,p[i]);
            c = o[i] - o1;
            if(c%d) z = 0;
            mod = p[i]/d;
            x = ((c/d*x)%mod+mod)%mod;
            o1 = p1*x + o1;
            p1 = p1*mod;
        }
        if(!z)
        printf("-1
");
        else
        printf("%I64d
",o1);
    }
    return 0;
}