POJ 1061 青蛙的约会（扩展欧几里得算法）

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<string>
 4 #include<cstring>
 5 #include<cmath>
 6 using namespace std;
 7 
 8 long long int x, y, m, n, l;
 9 
10 long long gcd(long long a, long long b)
11 {
12     return b == 0 ? a : gcd(b, a%b);
13 }
14 
15 void extend_gcd(long long a, long long b, long long& x, long long& y)
16 {
17     if (b == 0)
18     {
19         x = 1;
20         y = 0;
21         return;
22     }
23     else
24     {
25         extend_gcd(b, a%b, x, y);
26         long long int temp = x;
27         x = y;
28         y = temp - a / b*y;
29     }
30 }
31 
32 int main()
33 {
34     //freopen("D:\\txt.txt", "r", stdin);
35     while (cin >> x >> y >> m >> n >> l)
36     {
37         long long int a = n - m, b = l, c = x - y, p, q;
38         long long int d = gcd(a, b);
39         //如果c不能被d整除，肯定没有整数解
40         if (c%d)
41         {
42             cout << "Impossible" << endl;
43             continue;
44         }
45         extend_gcd(a, b, p, q);
46         p = p*c / d;
47         p = p%l;
48         if (p < 0)  p += l;
49         cout << p << endl;
50     }
51     return 0;
52 }