33 lines
749 B
C++
33 lines
749 B
C++
#include <bits/stdc++.h>
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using namespace std;
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#define int long long
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#define endl "\n"
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const int N = 3;
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int n, mod;
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// 矩阵乘法
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void mul(int a[][N], int b[][N], int c[][N]) {
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int t[N][N] = {0};
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for (int i = 0; i < N; i++) {
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for (int j = 0; j < N; j++)
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for (int k = 0; k < N; k++)
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t[i][j] = (t[i][j] + (a[i][k] * b[k][j]) % mod) % mod;
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}
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memcpy(c, t, sizeof t);
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}
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signed main() {
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int b[N][N] = {1, 1, 1};
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int m[N][N] = {
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{1, 0, 0},
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{1, 1, 1},
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{0, 1, 0}};
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cin >> n >> mod;
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// 矩阵快速幂
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for (int i = n - 1; i; i >>= 1) {
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if (i & 1) mul(b, m, b);
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mul(m, m, m);
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}
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printf("%d\n", b[0][0]);
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} |