题意:计算公式
题解:想推出矩阵相乘的形式,想了很久也想不出,然后看别人的题解有一个高中就学过的式子:
(1 + x) ^ n = Cn0x^n+Cn1x^(n-1)+Cn2x^(n-2)+Cn3x^(n-3)+····+Cnn
然后想到斐波那契矩阵是{1,1,1,0},1看做一个单位阵{1,0,1,0},就会做了。。。
#include <stdio.h>
#include <string.h>
int n, m;
struct Mat {
int g[2][2];
}ori, res;
Mat multiply(Mat x, Mat y) {
Mat temp;
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++) {
temp.g[i][j] = 0;
for (int k = 0; k < 2; k++)
temp.g[i][j] = (temp.g[i][j] + x.g[i][k] * y.g[k][j]) % m;
}
return temp;
}
void calc(int n) {
while (n) {
if (n & 1)
res = multiply(res, ori);
n >>= 1;
ori = multiply(ori, ori);
}
}
int main() {
int t;
scanf("%d", &t);
while (t--) {
scanf("%d%d", &n, &m);
ori.g[0][0] = 2;
ori.g[0][1] = ori.g[1][0] = ori.g[1][1] = 1;
res.g[0][0] = res.g[1][1] = 1;
res.g[0][1] = res.g[1][0] = 0;
calc(n);
printf("%d\n", res.g[0][1]);
}
return 0;
}