Problem p03168 (C++)

Buggy submission (status: Runtime Error):
// if acyclic graph try toposort
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define pb push_back
#define vll vector<ll>
#define pll pair<ll, ll>
#define vpll vector<pll>
#define ub upper_bound
#define lb lower_bound
#define all(v) ((v).begin()), ((v).end())
#define allr(v) ((v).rbegin()), ((v).rend())
#define ff first
#define ss second
#define mp make_pair
#define pll pair<ll, ll>
#define fo(i, n) for (ll i = 0; i < n; i++)
#define foa(i, s, e) for (ll i = (s); i < e; i++)
#define fod(i, s, e) for (ll i = (s); i >= (e); i--)
#define max3(a, b, c) max(max(a, b), c)
#define min3(a, b, c) min(min(a, b), c)
#define deb(x) cerr << #x << ' ' << '=' << ' ' << x << '\n'
#define sz(x) (ll)(x.size())
#define ANS cout << ans << '\n'
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define Yes cout << "Yes\n"
#define No cout << "No\n"
const ld pi = 3.14159265358979323846;
ll MOD = 1e9 + 7;
// ll MOD = 998244353;
const char nl = '\n';
const ll inf = 1e15;
#define fill(a, b) memset(a, b, sizeof(a))
#define setbits(x) __builtin_popcountll(x)
#define print2d(dp, n, m)                                                      \
  fo(i, n) {                                                                   \
    fo(j, m) cout << dp[i][j] << " ";                                          \
    cout << "\n";                                                              \
  }
template <typename T> void umax(T &a, T b) { a = max(a, b); }
template <typename T> void umin(T &a, T b) { a = min(a, b); }
ll nxt() {
  ll x;
  cin >> x;
  return x;
}
ll mul(ll x, ll y) { return (1ll * (x % MOD) * (y % MOD)); }
ll modpow(ll x, ll y) {
  ll z = 1;
  while (y > 0) {
    if (y % 2)
      z = mul(z, x);
    x = mul(x, x);
    y /= 2;
  }
  return z;
}
ll power(ll x, ll y) {
  ll z = 1;
  while (y > 0) {
    if (y % 2)
      z = z * x;
    x = x * x;
    y /= 2;
  }
  return z;
}
ll gcd(ll a, ll b) {
  if (a < b)
    return gcd(b, a);
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll sq(ll a) {
  ll ans = (1ll * a * a);
  return ans;
}
const ll N = 1e3 + 5;
ld dp[N];
void solve() {
  ll n;
  cin >> n;
  dp[0] = 1;
  fo(i, n) {
    ld p;
    cin >> p;
    for (ll j = i + 1; j >= 0; j--) {
      dp[j] = dp[j] * (1 - p) + (j ? dp[j - 1] * p : 0);
    }
  }
  // fo(i, n)cout << dp[i] << nl;
  ld ans = 0;
  fo(i, n + 1) {
    ll t = n - i;
    if (t < i) {
      ans += dp[i];
    }
  }
  cout << fixed << setprecision(10) << ans << nl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
#ifndef ONLINE_JUDGE
  freopen("inputf.txt", "r", stdin);
  freopen("outputf.txt", "w", stdout);
  freopen("error.txt", "w", stderr);
#endif
  ll TC = 1;
  // cin>>TC;
  while (TC--) {
    solve();
  }
  cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\n";
}


Fixed submission:
// if acyclic graph try toposort
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define pb push_back
#define vll vector<ll>
#define pll pair<ll, ll>
#define vpll vector<pll>
#define ub upper_bound
#define lb lower_bound
#define all(v) ((v).begin()), ((v).end())
#define allr(v) ((v).rbegin()), ((v).rend())
#define ff first
#define ss second
#define mp make_pair
#define pll pair<ll, ll>
#define fo(i, n) for (ll i = 0; i < n; i++)
#define foa(i, s, e) for (ll i = (s); i < e; i++)
#define fod(i, s, e) for (ll i = (s); i >= (e); i--)
#define max3(a, b, c) max(max(a, b), c)
#define min3(a, b, c) min(min(a, b), c)
#define deb(x) cerr << #x << ' ' << '=' << ' ' << x << '\n'
#define sz(x) (ll)(x.size())
#define ANS cout << ans << '\n'
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define Yes cout << "Yes\n"
#define No cout << "No\n"
const ld pi = 3.14159265358979323846;
ll MOD = 1e9 + 7;
// ll MOD = 998244353;
const char nl = '\n';
const ll inf = 1e15;
#define fill(a, b) memset(a, b, sizeof(a))
#define setbits(x) __builtin_popcountll(x)
#define print2d(dp, n, m)                                                      \
  fo(i, n) {                                                                   \
    fo(j, m) cout << dp[i][j] << " ";                                          \
    cout << "\n";                                                              \
  }
template <typename T> void umax(T &a, T b) { a = max(a, b); }
template <typename T> void umin(T &a, T b) { a = min(a, b); }
ll nxt() {
  ll x;
  cin >> x;
  return x;
}
ll mul(ll x, ll y) { return (1ll * (x % MOD) * (y % MOD)); }
ll modpow(ll x, ll y) {
  ll z = 1;
  while (y > 0) {
    if (y % 2)
      z = mul(z, x);
    x = mul(x, x);
    y /= 2;
  }
  return z;
}
ll power(ll x, ll y) {
  ll z = 1;
  while (y > 0) {
    if (y % 2)
      z = z * x;
    x = x * x;
    y /= 2;
  }
  return z;
}
ll gcd(ll a, ll b) {
  if (a < b)
    return gcd(b, a);
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll sq(ll a) {
  ll ans = (1ll * a * a);
  return ans;
}
const ll N = 3e3 + 5;
ld dp[N];
void solve() {
  ll n;
  cin >> n;
  dp[0] = 1;
  fo(i, n) {
    ld p;
    cin >> p;
    for (ll j = i + 1; j >= 0; j--) {
      dp[j] = dp[j] * (1 - p) + (j ? dp[j - 1] * p : 0);
    }
  }
  // fo(i, n)cout << dp[i] << nl;
  ld ans = 0;
  fo(i, n + 1) {
    ll t = n - i;
    if (t < i) {
      ans += dp[i];
    }
  }
  cout << fixed << setprecision(10) << ans << nl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
#ifndef ONLINE_JUDGE
  freopen("inputf.txt", "r", stdin);
  freopen("outputf.txt", "w", stdout);
  freopen("error.txt", "w", stderr);
#endif
  ll TC = 1;
  // cin>>TC;
  while (TC--) {
    solve();
  }
  cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\n";
}