51nod 1256 乘法逆元

#include <bits/stdc++.h>
using namespace std;

int extgcd(int a,int b,int &x,int &y)
{
    int d=a;
    if(b != 0){
        d = extgcd(b,a%b,y,x);
        y -= (a/b)*x;
    }
    else
    {
        x = 1, y = 0;
    }
    return d;
}

int mod_ny(int m,int n)  //求k * m = 1 (mod n)
{
    int x,y;
    extgcd(m,n,x,y);
    return (x%n + n) %n;//防止 x是负数
}

int main()
{
    int n,m;
    scanf("%d %d",&m,&n);
    printf("%d\n",mod_ny(m,n));
}