HDU 1005

此题关键是要发现周期性。


#include <stdio.h>
#include <string.h>

int f[1000];
int compute(int a, int b, int n)
{
    int i, cycle;
    memset(f, 0, 1000*sizeof(int));    

    f[1] = 1;
    f[2] = 1;
    for(i = 3; i < 1000; i++) {
        
        f[i] = (a * f[i-1] + b * f[i-2]) % 7;
        if(f[i-1] == 1 && f[i] == 1) {
            break;
        }
        printf("f[%d]=%d\n", i, f[i]);
    }
    cycle = i - 2;
    f[0] = f[cycle];
        
    return f[n % cycle];
}

int main(void)
{
    int a, b, n;
    while(scanf("%d %d %d", &a, &b, &n) && (0 != a && 0 != b && 0 != n)) { 
        
        printf("%d\n", compute(a, b, n));
    } 
}