2976. [Poi2002]出圈游戏

https://hydro.ac/d/bzoj/record/63a45f32cf75a716a1673915

BZOJ/2976/2976.cpp

@@ -0,0 +1,68 @@
+#include <iostream>
+#include <algorithm>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 25;
+
+int n, a[N], p[N], d[N], m[N];
+
+long long exgcd(long long a, long long b, long long& x, long long& y) {
+    if (!b) {
+        x = 1;
+        y = 0;
+        return a;
+    }
+
+    long long g = exgcd(b, a % b, y, x);
+    y -= a / b * x;
+    return g;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        p[a[i]] = i;
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = p[i - 1]; j != p[i]; j = j == n ? 1 : j + 1) {
+            if (a[j] > i) d[i]++;
+        }
+
+        m[i] = n - i + 1;
+        d[i] = (d[i] + 1) % m[i];
+    }
+
+    long long res = d[1], lcm = m[1];
+    for (int i = 2; i <= n; i++) {
+        long long x, y,
+            g = exgcd(lcm, m[i], x, y),
+            c = ((d[i] - res) % m[i] + m[i]) % m[i],
+            m1 = m[i] / g,
+            m2 = lcm / g * m[i];
+
+        if (c % g) {
+            cout << "NIE" << endl;
+
+            exit(0);
+        }
+
+        x = (x % m[i] + m[i]) % m[i];
+        x = (x * c / g % m1 + m1) % m1;
+        res = ((lcm * x + res) % m2 + m2) % m2;
+        lcm = m2;
+    }
+
+    cout << (res ? res : lcm) << endl;
+
+    return 0;
+}