提出 #20791455

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ソースコード 拡げる

#include <atcoder/all>
using namespace atcoder;
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const double pi = 3.14159265359;
const ll INF = 1LL << 60;

double dpa[200020];
double dpb[200020];

bool hole[100001];

int main()
{
  int n, m, k;
  cin >> n >> m >> k;
  for (int i = 0; i < k; i++){
    int a;
    cin >> a;
    hole[a] = true;
  }

  int ct = 0;
  for (int i = 1; i < n; i++){
    if (hole[i]){
      ct++;
      if (ct >= m){
	cout << -1 << endl;
	return 0;
      }
    } else {
      ct = 0;
    }
  }
  
  double suma = 0, sumb = 0;
  for (int i = n-1; i >= 0; i--){
    if (hole[i]){
      dpa[i] = 1.0;
      dpb[i] = 0.0;
    } else {
      dpa[i] = suma / double(m);
      dpb[i] = sumb / double(m) + 1.0;
    }
    suma += dpa[i] - dpa[i+m];
    sumb += dpb[i] - dpb[i+m];
  }

  double ans = dpb[0] / (1 - dpa[0]);
  cout << fixed << setprecision(4) << ans << endl;
  return 0;
}

提出情報

ジャッジ結果