【java每日一题，数论】最大公约数，最大质因数，欧拉筛

int a=s.nextInt();
int b=s.nextInt();
int c,d;
while (true){
    if(a>b){
        c=a;
        d=b;
    }else {
        c=b;
        d=a;
    }
    a=c%d;
    b=d;
    if(a==0){
        System.out.println(b);
        break;
    }
}

int n=s.nextInt();
int i,ans=0;
for( i=2;i*i<=n;i++){
    while (n%i==0){
        ans=i;
        n/=i;
    }
}
if(n>1){
    ans=n;
}
System.out.println(ans);

int n=s.nextInt();
int k = 2; 
while (n > 1){
    if (n % k == 0){
        n /= k;
    }
    else{
        k++; 
    }
}
System.out.println(ans);

int n=s.nextInt();
int[] primes=new int[n+1];
boolean[] st=new boolean[n+1];
int count=0;
for(int i=2;i<=n;i++){
  if(!st[i])primes[count++]=i;
  for(int j=0;i*primes[j]<=n;j++){
    st[i*primes[j]]=true;
    if(i%primes[j]==0)break;
  }
}
System.out.println(Arrays.toString(primes));