JSOI2009 BZOJ2257 瓶子和燃料

想法其实是挺巧妙的。。找到所有数的所有因数，统计最大的一个出现过K次的因数。

Code:

#include <cstdio>
#include <iostream>

using namespace std;

long a[1001];
long s[1000001];

long gcd(long a,long b){
	if (a%b==0) {
		return b;
	}
	if (b%a==0) {
		return a;
	}
	return gcd(b,a%b);
}
void qqsort(long l,long r){
	long i=l,j=r,x;
	x=s[(l+r)/2];
	/*cout <<l <<" " <<r <<endl;*/
	long t;
	while (i<=j){
		while (s[i]<x){
			i++;
		}
		while (x<s[j]){
			j--;
		}
		if (i<=j){
			t=s[i];s[i]=s[j];s[j]=t;
			i++;j--;
		}
	}
	if (i<r){
		qqsort(i,r);
	}
	if (j>l){
		qqsort(l,j);
	}
}

int main(){
	/*freopen("bottle.in", "r", stdin) ;
	freopen("bottle.out", "w", stdout) ;*/
	long n,k;
	cin >>n >>k;
	for (long i=1;i<=n;i++){
		cin>>a[i];
	}
	long r=0;
	for (long i=1;i<=n;i++){
	    for (long j=1;j*j<=a[i];j++){
			if (a[i]%j==0){
				r++;s[r]=j;
				//cout <<s[r] <<endl;
				r++;s[r]=a[i]/j;
				//cout <<s[r] <<endl;
			}
	    }
	}
	qqsort(1,r);
	long app=1;
	for (long i=r-1;i>0;i--){
		if (s[i]==s[i+1]){
			app++;
		}
		else
		{
			app=1;
		}
		if (app>=k){
			cout <<s[i] <<endl;
			break;
		}
	}
	/*cin >>n;*/
}