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## HDOJ 1005 Number Sequence

Wu Yudong    August 19, 2018     HDOJ   415

Problem Description
A number sequence is defined as follows:

f(1) = 1, f(2) = 1, f(n) = (A * f(n - 1) + B * f(n - 2)) mod 7.

Given A, B, and n, you are to calculate the value of f(n).

Input
The input consists of multiple test cases. Each test case contains 3 integers A, B and n
on a single line (1 <= A, B <= 1000, 1 <= n <= 100,000,000). Three zeros signal the end
of input and this test case is not to be processed.

Output
For each test case, print the value of f(n) on a single line.

Sample Input
1 1 3
1 2 10
0 0 0

Sample Output
2
5


#include <stdio.h>
#include<math.h>

int main()
{
int a, b, i;
long n, num[50];
num[1] = num[2] = 1;
while (scanf("%d %d %ld", &a, &b, &n), a + b + n) {
for (i = 3; i <= 48; i++)
num[i % 48] = (a * num[i - 1] + b * num[i - 2]) % 7;
printf("%ld\n", num[n % 48]);
}
return 0;
}