3n_1.c

#include <stdio.h>
#define swap(x,y) int t=x;x=y;y=t;
typedef unsigned long long ull;
ull foo(int a,int b){
    ull cycle;
    ull c,n;
    ull max = 0;
    if(a>b){
        swap(a,b)
    }
    for(c=a;c<=b;c++){
        cycle = 1;
        n = c;
        while(n!=1){
            n = n%2==1?3*n+1 : n/2;
            cycle ++;
        }
        if(cycle>max){
            max = cycle;
        }
    }
    return max;
}
int main(int argc, const char * argv[])
{
    int a,b;
    while(scanf("%d%d",&a,&b)!=EOF){
        printf("%d %d %llu\n",a,b,foo(a, b));
    }
    return 0;
}