題目

https://www.luogu.org/problemnew/show/P1082

程式碼

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll a, b, x, y;
inline ll read()
{
	ll f=1,num=0;
	char ch=getchar();
	while (ch<'0'||ch>'9') { if (ch=='-') f=-1; ch=getchar(); }
	while (ch>='0'&&ch<='9'
 
) num=(num<<1)+(num<<3)+ch-'0',ch=getchar();
	return num*f;
}
void gcd(ll a,ll b,ll &x,ll &y)
{
    if (!b)
    {
        x=1,y=0;
        return;
    }
    gcd(b,a%b,x,y);
    ll tmp=x;
    x=y;
	y=tmp-a/b*y;
}

int main()
{
    a=read(),b=read();
    gcd(a,b,x,y);
    x = (x%b+b)%
 
b;
    printf("%lld\n",x);
    return 0;
}