csust 1097

最新推荐文章于 2022-01-03 19:59:37 发布

原创最新推荐文章于 2022-01-03 19:59:37 发布 · 158 阅读

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ai = (p^2)*k1; aj = (q^2)*k2;

当且仅当k1 == k2时 ai*aj为完全平方数

#include"cstdio"
#include"cstring"
#include"iostream"
#include"algorithm"
using namespace std;
typedef long long LL;
const int maxn = 1e6+100;

bool is_prime[maxn];
int prime[maxn],tot,x,cnt[maxn],id[maxn];

void get_prime()
{
    int n = 1e6+99;
    for(int i = 2; i <= n; i++){
        if(!is_prime[i]) prime[++tot] = i;
        for(int j = 1; j <= tot; j++){
            if(i*prime[j] > n) break;
            is_prime[i*prime[j]] = 1;
            if(i%prime[j] == 0) break;
        }
    }
    for(int i = 1; prime[i-1] <= n; i++){
        prime[i]*=prime[i];
    }
    for(int i = 1; i <= n; i++){
        int x = i;
        for(int j = 1; prime[j] <= x; j++){
            while(x%prime[j] == 0)
                x /= prime[j];
        }
        id[i] = x;
    }
}
int main()
{
#ifdef __LOCAL__
    freopen("input.txt","r",stdin);
#endif // __LOCAL
    int n;
    get_prime();
    while(~scanf("%d",&n)){
        int maxx = 0;
        for(int i = 1,x; i <= n; i++){
            scanf("%d",&x);
            maxx = max(maxx,id[x]);
            cnt[id[x]]++;
        }
        LL ans = 0;
        for(int i = 0; i <= maxx; i++){
            ans += (LL) cnt[i]*(cnt[i]-1)/2;
            cnt[i] = 0;
        }
        cout<<ans<<endl;
    }
    return 0;
}