ACM 371 Ackermann Functions

吃了3個WA以後，去找解答才知道這題有兩個陷阱= =
(1) L有可能大於H
(2) 題目說不會大於long的意思是指不會大於unsigned long


#include <stdio.h>

int main(void)
{
    long long L, H, n, num;
    int c, max;
   
    while (scanf("%lld%lld", &L, &H) == 2 && (L || H))
    {
        if (L > H)
        {
            n = H;
            H = L;
            L = n;
        }
        printf("Between %lld and %lld, ", L, H);
        max = 0;
        for (; L <= H; L++)
        {
            c = 0;
            n = L;
            do {
                if (n % 2)
                    n = 3*n+1;
                else
                    n /= 2;
                c++;
            } while (n != 1);
            if (c > max)
            {
                max = c;
                num = L;
            }
        }
        printf("%lld generates the longest sequence of %d values.\n", num, max);
    }

    return 0;
}