HDU 2685 I won't tell you this is about number theory
题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=2685
题意:求gcd(a^m - 1, a^n - 1) mod k
思路:gcd(a^m - 1, a^n - 1) = a^gcd(m, n) - 1
code:
1 #include <stdio.h> 2 3 int gcd(int a, int b) 4 { 5 return !b ? a : gcd(b, a%b); 6 } 7 8 int mod_pow(int a, int x, int mod) 9 { 10 int tmp = a; 11 int ret = 1; 12 while(x) { 13 if (x & 1) { 14 ret = ret * tmp % mod; 15 } 16 tmp = tmp * tmp % mod; 17 x >>= 1; 18 } 19 20 return ret; 21 } 22 23 int main() 24 { 25 int t, a, m, n, k; 26 scanf("%d", &t); 27 while (t--) { 28 scanf("%d %d %d %d", &a, &m, &n, &k); 29 int d = gcd(m, n); 30 int ans = mod_pow(a, d, k); 31 printf("%d\n", (ans - 1 + k) % k); 32 } 33 34 return 0; 35 }