hdu 1576 A/B (求逆元)

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <cmath>
 6 #include <algorithm>
 7 #define LL __int64
 8 const int maxn = 1e3 + 10;
 9 const int mo = 9973;
10 using namespace std;
11 
12 void exgcd(LL a, LL b, LL &d, LL &x, LL &y)
13 {
14     if(!b) {d = a; x = 1; y = 0;}
15     else{ exgcd(b, a%b, d, y, x); y -= x*(a/b); }
16 }
17 
18 LL mo_reve(LL a, LL n)
19 {
20     LL x, y;
21     LL d;
22     exgcd(a, n, d, x, y);
23     if(d==1) return (x%n+n)%n;
24     else return -1;
25 }
26 
27 int main()
28 {
29      int t, n, b;
30      scanf("%d", &t);
31      while(t--)
32      {
33          scanf("%d%d", &n, &b);
34          int x = mo_reve(b, mo);
35          printf("%d\n", n*x%mo);
36      }
37      return 0;
38 }