题目:

题解:

线性同余方程

#include <bits/stdc++.h>
using namespace std;
long long exgcd(long long a,long long b,long long &x,long long &y)
{
    if (!b)
    {
        x = 1, y = 0;
        return a;
    }
    long long  d = exgcd(b, a % b, x, y);
    long long  z = x;
    x = y;
    y = z - a / b * y;
    return d;
}
int main()
{
    long long a,b,m,x,y;
    scanf("%lld %lld",&a,&m);
    b=1;
    long long d=exgcd(a,m,x,y);
    {
        x=(x*b/d%m+m)%m;
        cout<<x<<endl;
    }
    return 0;
}