j.cpp

j.cpp

@@ -0,0 +1,84 @@
+//Question Link https://atcoder.jp/contests/dp/tasks/dp_j
+#include <bits/stdc++.h>
+#include <cstring>
+#include <limits>
+//author Bhaskar Joshi
+using namespace std;
+#define ll long long int
+#define X first
+#define Y second
+#define fw(i, start, end) for (ll i = start; i < end; ++i)
+#define fe(i, start, end) for (ll i = start; i <= end; ++i)
+#define L(T)  \
+    ll T;     \
+    cin >> T; \
+    while (T--)
+#define FASTIO                   \
+    ios::sync_with_stdio(false); \
+    cin.tie(nullptr);            \
+    cout.tie(nullptr);
+#define endl '\n'
+
+double dp[302][302][302];
+double ev[302][302][302];
+
+int main()
+
+{
+    FASTIO
+    ll n;
+    cin >> n;
+    ll
+        a[n + 5];
+    int one = 0, two = 0, three = 0;
+    fe(i, 1, n)
+    {
+        cin >> a[i];
+        if (a[i] == 1)
+            one++;
+        if (a[i] == 2)
+        {
+            two++;
+        }
+        if (a[i] == 3)
+            three++;
+    }
+    memset(dp, -1, 0);
+    // cout << "one  " << one << "  two  " << two << "  three  " << three << endl;
+    dp[one][two][three] = 1;
+    for (ll k = n; k >= 0; k--)
+    {
+        for (ll j = n; j >= 0; j--)
+        {
+            for (ll i = n; i >= 0; i--)
+            {
+                if (i == 0 && j == 0 && k == 0)
+                    continue;
+                if (i + j + k > n)
+                    continue;
+                double pw = (double)(n - (i + j + k)) / n;
+                double ew = pw / (1 - pw) + 1;
+                ev[i][j][k] += ew * dp[i][j][k];
+                if (i != 0)
+                {
+                    dp[i - 1][j][k] += (double)((double)(dp[i][j][k] * i) / (i + j + k));
+                    ev[i - 1][j][k] += (double)((double)(ev[i][j][k] * i) / (i + j + k));
+                }
+                if (j != 0)
+                {
+                    dp[i + 1][j - 1][k] += (double)((double)(dp[i][j][k] * j) / (i + j + k));
+                    ev[i + 1][j - 1][k] += (double)((double)(ev[i][j][k] * j) / (i + j + k));
+                }
+                if (k != 0)
+                {
+                    dp[i][j + 1][k - 1] += (double)((double)(dp[i][j][k] * k) / (i + j + k));
+                    ev[i][j + 1][k - 1] += (double)((double)(ev[i][j][k] * k) / (i + j + k));
+                }
+            }
+        }
+    }
+    double ans = ev[0][0][0];
+    // cout << ans << "\n";
+    printf("%.10lf\n", ans);
+    return 0;
+}