pku2115 C Looooops

http://poj.org/problem?id=2115

数论，模线性方程

 1 #include <stdio.h>
 2 #include <vector>
 3 
 4 using namespace std;
 5 
 6 long long extend_gcd(long long a, long long b, long long &x, long long &y)
 7 {
 8     if(b == 0)
 9     {
10         x = 1;
11         y = 0;
12         return a;
13     }
14     long long r = extend_gcd(b, a%b, y, x);
15     y -= x*(a/b);
16     return r;
17 }
18 
19 long long line_mod_equation(long long a, long long b, long long n)
20 {
21     long long x, y;
22     long long d = extend_gcd(a, n, x, y);
23     if(b%d == 0)
24     {
25         x %= n;
26         x += n;
27         x %= n;
28         x = x*(b/d)%(n/d);  //最小解
29         x = (x%(n/d)+n/d)%(n/d);//最小正整数解
30         return x;
31     }
32     else
33     {
34         return -1;
35     }
36 }
37 
38 int main()
39 {
40     long long A, B, C, K;
41     long long a, b, n, i, j, r;
42     while(scanf("%lld%lld%lld%lld", &A, &B, &C, &K), A||B||C||K) 
43     {
44         a = C;
45         b = B - A;
46         n = (long long)1 << K;
47         r = line_mod_equation(a, b, n);
48         if(r == -1)
49         {
50             printf("FOREVER\n");
51         }
52         else
53         {
54             printf("%lld\n", r);
55         }
56     }
57     return 0;
58 }

 

posted @ 2013-05-25 16:36  Yuan1991  阅读(116)  评论(0)  编辑  收藏  举报