[PHP] bzoj2038 [2009国家集训队]小Z的袜子(hose)

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long ll;
const ll maxn = 500010;
struct node
{
  ll l,r,id;
}e[maxn];
ll n,m,a[maxn],block,L = 1,R = 0;
ll ans,tong[maxn],fenzi[maxn],fenmu[maxn];
bool cmp(node a,node b)
{
  if (a.l / block == b.l / block)
    return a.r < b.r;
  return (a.l / block) < (b.l / block);
}
ll gcd(ll a,ll b)
{
  if (b == 0)
    return a;
  return gcd(b,a % b);
}
ll C(ll x)
{
  return x * (x - 1) / 2;
}
void update1(ll pos) //删
{
  tong[a[pos]]--;
  ans -= tong[a[pos]];
}
void update2(ll pos) //加
{
  ans += tong[a[pos]];
  tong[a[pos]]++;
}
int main()
{
  scanf("%lld%lld",&n,&m);
  block = sqrt(n);
  for (ll i = 1; i <= n; i++)
    scanf("%lld",&a[i]);
  for (ll i = 1; i <= m; i++)
  {
    scanf("%lld%lld",&e[i].l,&e[i].r);
    e[i].id = i;
  }
  sort(e + 1,e + 1 + m,cmp);
  for (ll i = 1; i <= m; i++)
  {
    ll l = e[i].l,r = e[i].r;
    while (R < r)
      update2(++R);
    while (L > l)
      update2(--L);
    while (L < l)
      update1(L++);
    while (R > r)
      update1(R--);
    fenzi[e[i].id] = ans;
    fenmu[e[i].id] = C(r - l + 1);
  }
  for (ll i = 1; i <= m; i++)
  {
    if (!fenzi[i])
    {
      printf("0/1\n");
      continue;
    }
    ll temp = 1;
    temp = gcd(fenzi[i],fenmu[i]);
    fenzi[i] /= temp;
    fenmu[i] /= temp;
    if (fenzi[i] == 0)
      fenmu[i] = 1;
    printf("%lld/%lld\n",fenzi[i],fenmu[i]);
  }
  return 0;
}