1304. 佳佳的斐波那契

https://www.acwing.com/problem/content/submission/code_detail/7249810/

AcWing/1304/1304.cpp

@@ -0,0 +1,37 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, k;
+
+void mul(int c[][4], int a[][4], int b[][4]) {
+    int t[4][4];
+    memset(t, 0x00, sizeof(t));
+    for (int i = 0; i < 4; i++) {
+        for (int j = 0; j < 4; j++) {
+            for (int k = 0; k < 4; k++) {
+                t[i][j] = (t[i][j] + 1ll * a[i][k] * b[k][j]) % m;
+            }
+        }
+    }
+    memcpy(c, t, sizeof(t));
+}
+
+int main() {
+    cin >> n >> m;
+    k = n - 1;
+    int f[4][4] = {1, 1, 1, 0};
+    int a[4][4] = {
+        {0, 1, 0, 0},
+        {1, 1, 1, 0},
+        {0, 0, 1, 1},
+        {0, 0, 0, 1},
+    };
+    while (k) {
+        if (k & 1) mul(f, f, a);
+        mul(a, a, a);
+        k >>= 1;
+    }
+    cout << ((1ll * n * f[0][2] - f[0][3]) % m + m) % m << endl;
+    return 0;
+}