51nod 1256 乘法逆元 拓展欧几里得求逆元

#include <iostream>
#include <cstdio>

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_inv(int a, int m){
    int x, y;
    extgcd(a, m, x, y);
    return (m+x%m)%m;
}
int main() {
    int n, m;
    scanf("%d%d", &m, &n);
    printf("%d\n", mod_inv(m, n));
    return 0;
}