uva_cpp_clean/100/100-21.cpp

/*
  >>~~ UVa Online Judge ACM Problem Solution ~~<<

  ID: 100
  Name: The 3n + 1 problem
  Problem: https://onlinejudge.org/external/1/100.pdf
  Language: C++

  Author: Arash Shakery
  Email: [email protected]
*/

#include <stdio.h>
#include <iostream>
using namespace std;

#define MAX 10000000
long long int memo[MAX];
long long int alen(long long int n, int d) {
    if (n == 1) return 1;
    if (!d || n<0) return -1e7;
    if (n < MAX && memo[n]) return memo[n];

    long long int x = n;
    int b = 0;
    for (; !(x&1); x>>=1)
        b++;


    long long int r = 1;
    if (x < MAX && memo[x])
        r = memo[x];

    else if (x>1 && 3*x+1>0) {
        r = alen(3*x + 1, d-1) + 1;
        if (x < MAX && r>0) memo[x] = r;
    }

    if (n < MAX && r>0) memo[n] = b + r;
    return b + r;
}

int main(){
    bool b;
    long long int l, r;
    while (cin>>l>>r && (l||r)) {
        long long int best = 0;
        if ((b = r < l)) {
            r ^= l;
            l ^= r;
            r ^= l;
        }

        for (long long int i=r; i>=l; i--) {
            long long int al = alen(i, 800);
            if (al >= best) best = al;
        }

        printf("%lld %lld %lld\n", b?r:l, b?l:r, best);
    }
}