P1082 同余方程（扩欧模板）

https://www.luogu.org/problem/P1082

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(int i=a;i<=b;++i)
//by war
//2019.8.7
using namespace std;
int a,b,x,y;
void in(int &x){
    int y=;char c=getchar();x=;
    while(c<''||c>''){if(c=='-')y=-;c=getchar();}
    while(c<=''&&c>=''){ x=(x<<)+(x<<)+c-'';c=getchar();}
    x*=y;
}
void o(int x){
    if(x<){p('-');x=-x;}
    if(x>)o(x/);
    p(x%+'');
}

void exgcd(int a,int b,int &x,int &y){
    if(!b){
        x=;y=;
        return;
    }
    exgcd(b,a%b,y,x);
    y-=a/b*x;
}

signed main(){
    in(a);in(b);
    exgcd(a,b,x,y);
    o((x%b+b)%b);
    return ;
}