乘法逆元(扩展欧几里得)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#define ll long long
using namespace std;
ll n,p;
void exgcd(ll a,ll b,ll &x,ll &y)
{
    if(!b)
    {
        x=1;y=0;
        return;
    }
    exgcd(b,a%b,x,y);
    ll tmp=x;
    x=y;
    y=tmp-a/b*y;
}
int main()
{
    scanf("%lld%lld",&n,&p);
    ll x=0,y=0;
    exgcd(n,p,x,y);
    x=(x%p+p)%p;
    printf("%lld\n",x);
    return 0;
}