复习1 数论

#include<cstdio>
using namespace std;
int a,b;
int gcd(int x,int y){
    if(y==0)return x;
    return gcd(y,x%y);
}
int main(){
    scanf("%d%d",&a,&b);
    printf("%d",gcd(a,b));
}

#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
#define ll long long
ll a,b,x,y;
ll exgcd(ll a,ll b){
    if(b==0){
        x=1;y=0;
        return a;
    }
    exgcd(b,a%b);
    ll tmp=x;
    x=y;y=tmp-(a/b)*y;
}
int main(){
    scanf("%lld%lld",&a,&b);
    exgcd(a,b);
    while(x<0)x+=b;
    cout<<x;
}

void prepare(){
    for(int i=2;i<=n;i++){
        if(!vis[i])p[++cnt]=i;
        for(int j=1;j<=cnt&&i*p[j]<=n;j++){
            vis[i*p[j]]=1;
            if(i%p[j]==0)break;
        }
    }
}

int euler_phi(int n){//单个欧拉函数 
    int m=(int)sqrt(n+0.5);
    int ans=n;
    for(int i=2;i<=m;i++)if(n%i==0){
        ans=ans/i*(i-1);
        while(n%i==0)n/=i;
    }
    if(n>1)ans=ans/n*(n-1);
}