Approximate

// NONAME-01
 
#include <bits/stdc++.h>
 
 
using namespace std;
 
vector <int> a;
vector <long long> x;
vector <long long> xx;
int n, m;
 
void Load()
{
	cin >> n >> m;
	int i;
	a.resize(n); x.resize(n); xx.resize(n);
	for (i = 0; i < n; i++) {
		cin >> a[i];
		if (i > 0) x[i] += x[i-1];
		x[i] += a[i];
		if (i > 0) xx[i] += xx[i-1];
		xx[i] += a[i]*a[i];
	}
}
 
void Solve()
{
  int i, a, b;
  for (i = 0; i < m; i++) {
	  cin >> a >> b;
	  a--;
	  b--;
	  long long s, ss;
	  s = x[b];
	  if (a > 0) s -= x[a-1];
	  ss = xx[b];
	  if (a > 0) ss -= xx[a-1];
	  long double l = b-a+1;
	 // cerr << s << ' ' << ss << ' ' << l << "\n";
	  long double ans = 1/l * (ss - s*(s/l));
	  cout.precision(6);
	  cout.setf(ios::fixed);
	  cout << ans << "\n";
	  
  }
  
}
 
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  Load();
  Solve();
  return 0;
}

Test 1

Verdict: ACCEPTED