#include <iostream>
#include <cmath>
using namespace std;

__int64 x, y;
__int64 x11, y11;
__int64 bit;
__int64 circle;
__int64 ans;
__int64 E_Euclid(__int64 a, __int64 c)
{
	__int64 q, r;
	q = a/c;
	r = a%c;
	if (r == 0)
		return c;
	__int64 t;
	t = x11;
	x11 = x;
	x = t - q*x;
	t = y11;
	y11 = y;
	y = t - q*y;
	a = c;
	c = r;
	return E_Euclid(a, c);
}

int main()
{
	__int64 a, b, c, k;
	while (1) {
		scanf("%I64d %I64d %I64d %I64d", &a, &b, &c, &k);
		if (a==0 && b==0 && c==0 && k==0)
			break;
		if (c==0 && a!=b) {
			printf("FOREVER\n");
			continue;
		}
		if (c==0 && a==b) {
			printf("0\n");
			continue;
		}
		bit = 1;
		bit = (__int64)(1<<k);
		x11 = y = 1;
		y11 = x = 0;
		int change = 0, add = 0;
		if (a<c) {
			swap(a,c);
			change = 1;
			if (c == 0) {
				add = 1;
				c += a;
			}
		}
		__int64 gcd = E_Euclid(a, c);
		int cc=0;
		if (b==0) {
			b += bit;
			cc = 1;
		}
		//cout<<a<<"*"<<x<<" + "<<c<<"*"<<y<<" = "<<gcd<<endl;
		x *= b/gcd;
		y *= b/gcd;
		//cout<<a<<"*"<<x<<" + "<<c<<"*"<<y<<" = "<<b<<endl;
		if ((a*x+c*y) != b)
			printf("FOREVER\n");
		else {
			if (!change) {
				
				ans = (y + a*(x-1)/c);
				//cout<<a<<" + "<<c<<"*"<<ans<<" = "<<b<<endl;
				if (ans < 0) {
					if ((a+c*ans) == b) {
						ans = (b+bit-a)/c;
						printf("%I64d\n", ans);
					}
					else
						printf("FOREVER\n");
				}
				else if ((a+c*ans)==b)
					printf("%I64d\n", ans);
				else
					printf("FOREVER\n");
			}
			else {
				ans = (x + c*(y-1)/a);
				if (ans < 0) {
					if ((c+a*ans) == b) {
						ans = (b+bit-c)/a;
						if (add)
							printf("%I64d\n", ans+1);
						else
							printf("%I64d\n", ans);
					}
					else
						printf("FOREVER\n");
				}
				else if (c+a*ans==b) {
					if (add)
						printf("%I64d\n", ans+1);
					else
						printf("%I64d\n", ans);
				}
				else
					printf("FOREVER\n");
			}
		}
	}
	return 0;
}
/*
#include <iostream>
using namespace std;

int main()
{
	int n;
	while (cin>>n)
		cout<<(1<<n)<<endl;
}*/

• 您的代码过于冗长了，贴一个我 AC 了的吧 (1280) IceKingdom 2009-07-20 11:58:02