Problem hidden
This problem was hidden by Editorial Board member probably because it has incorrect language version or invalid test data, or description of the problem is not clear.

Problem hidden on 2013-08-04 04:58:30 by Mitch Schwartz

PROBTRES - The 3n plus 1 problem V2

no tags 

Problems in Computer Science are often classified as belonging to a certain class of problems (e.g., NP, Unsolvable, Recursive). In this problem you will be analyzing a property of an algorithm whose classification is not known for all possible inputs.

The Problem:

Consider the following algorithm:

1. input n

2. print n

3. if n = 1 then STOP

4. if n is odd then n = 3n + 1

5. else n = n / 2

6. GOTO 2

Given the input 22, the following sequence of numbers will be printed 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1

It is conjectured that the algorithm above will terminate (when a 1 is printed) for any integral input value. Despite the simplicity of the algorithm, it is unknown whether this conjecture is true. It has been verified, however, for all integers n such that 0 < n < 1,000,000 (and, in fact, for many more numbers than this.)

Given an input n, it is possible to determine the number of numbers printed (including the 1). For a given n this is called the cycle-length of n. In the example above, the cycle length of 22 is 16.

For any two numbers i and j you are to determine the maximum cycle length over all numbers between i and j.

The Input:
The input will consist of a series of pairs of integers i and j, one pair of integers per line. All integers will be less than 1,000,000 and greater than 0.

You should process all pairs of integers and for each pair determine the maximum cycle length over all integers between and including i and j.

You can assume that no operation overflows a 32-bit integer.

The Output:
For each pair of input integers i and j you should output i, j, and the maximum cycle length for integers between and including i and j. These three numbers should be separated by at least one space with all three numbers on one line and with one line of output for each line of input. The integers i and j must appear in the output in the same order in which they appeared in the input and should be followed by the maximum cycle length (on the same line).

Sample Input:
1 10
100 200
201 210
900 1000

Sample Output:
1 10 20
100 200 125
201 210 89
900 1000 174

hide comments
behzad_nouri: 2016-02-18 02:49:36

The tests for this problem are **wrong**. You have to use **32-bit Unsigned** integers to force overflow in order to pass the tests. also, mentioned in

Last edit: 2016-02-18 02:50:07
Eros Smith: 2014-06-16 19:27:45

I am getting AC on simpler version and WA on this one using python 2.7. Anyone know what the issue might be considering the language is type-less?

Mitch Schwartz: 2013-08-04 02:58:36

Based on previous comments, you should be able to get AC with a 64-bit container if you take only the 32 least significant bits after each operation (i.e. perform operations mod 2^32). Anyway, the problem is hidden.

Raziman T V: 2013-08-03 23:46:40

The assumption that intermediate values do not overflow 32 bit range is wrong. As a result, test data is faulty. Using unsigned int in c++ gives AC whereas using long long gives WA.

Hossam El-Deen Goodname: 2013-06-13 07:44:03


The input terminates with EOF (end of file). You can google how to check for EOF using cin or scanf.

Last edit: 2013-06-13 07:44:16
Rahul: 2012-09-20 07:31:57

how does the input terminate?

Adrian Maceiras: 2012-09-05 01:57:34

Its that it doesnt overflow an unsigned int... java only provides signed int.

Jakub ©afin: 2012-02-01 14:06:23

also known as the Collatz sequence

James Broman: 2012-01-29 18:44:10

I am having issues with Java for V2. It is not getting accepted while I am able to get it working for V1.

What data types are you guys using for V2? What exactly is the difference between V1 and V2?

Saurajit: 2012-01-29 10:28:34

I'm having the same issue - I get AC for the simpler version, but WA for this one, even though I'm using unsigned long.

Added by:Coach UTN FRSF
Time limit:0.377s-3.779s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: ERL JS-RHINO PERL6