Collatz conjecture
Note: There is an ongoing discussion on removing this draft task in favour of Hailstone sequence. Please give your opinion, but DO NOT add to this page as it is likely to go away.
These programs calculate the Collatz sequence for a given integer, and stop if 1 is reached.
These programs were written before this task was created; as such, the specific actual requirements of this task have not yet been determined.
ALGOL 68
- note: This specimen retains the original Python coding style.
"as it is likely to go away" ... OOPS... translation was so easy I couldn't resist! :-) <lang algol68> main: (
INT n; read(n); print((n,":")); FOR i WHILE n > 1 DO n:=IF ODD n THEN n*3 + 1 ELSE n OVER 2 FI; print(" "+whole(n,0)) OD; print(new line)
)</lang> Input: 27
Output:
+27: 82 41 124 62 31 94 47 142 71 214 107 322 161 484 242 121 364 182 91 274 137 412 206 103 310 155 466 233 700 350 175 526 263 790 395 1186 593 1780 890 445 1336 668 334 167 502 251 754 377 1132 566 283 850 425 1276 638 319 958 479 1438 719 2158 1079 3238 1619 4858 2429 7288 3644 1822 911 2734 1367 4102 2051 6154 3077 9232 4616 2308 1154 577 1732 866 433 1300 650 325 976 488 244 122 61 184 92 46 23 70 35 106 53 160 80 40 20 10 5 16 8 4 2 1
Befunge
<lang befunge>&>:.:1-|
>3*^ @ |%2: < v>2/>+</lang>
C
<lang c>#include <stdio.h>
- include <stdlib.h>
int collatz( int n ) {
printf( "%i\n", n );
if( n == 1 ) return 1; else { if( (n % 2) == 0 ) return collatz( n / 2 ); else return collatz(1 + (n * 3)); } return 1;
}
int main( int argc, char** argv ) {
int n = atoi( argv[1] ); int i = collatz( n ); printf( "%i\n", i );
return 0;
}</lang>
C++
<lang cpp>#include <iostream> using namespace std;
int main() {
int n; cin >> n;
while (n > 1) {
if (n%2 != 0) { n = n*3 + 1; } else { n = n/2; } cout << n << endl;
}
}</lang>
Clojure
<lang lisp>(defn collatz [n] (take-while identity (iterate #(cond (even? %) (/ % 2) (= % 1) nil :else (inc (* % 3))) n)))
(collatz (read-string (read-line)))</lang>
Common Lisp
<lang lisp>(defun collatz (n)
(format t "~a~%" n) (cond ((= n 1) 1) ((= (mod n 2) 0) (collatz (/ n 2))) (t (collatz (+ 1 (* n 3))))))
(collatz (read))</lang>
Excel
In cell A1, place the starting number. In cell A2 enter this formula =IF(A1/2=ROUND(A1/2,0),A1/2,A1*3+1) Drag and copy the formula down until 4, 2, 1
Fortran
<lang fortran>program main
integer(4) :: n,i
write(6,*) "Input a natural number: " read (6,*) n
do while(n.gt.1) if(mod(n,2).eq.0) then ! number is even n=n/2 else ! number is odd n=3*n +1 endif write(6,*) n enddo
end program main</lang>
Haskell
<lang haskell>collatz :: Integer -> Integer collatz n
| n == 1 = 1 | even n = collatz (n `div` 2) | otherwise = collatz (3 * n + 1)</lang>
Ioke
<lang ioke>collatz = method(n,
n println unless(n <= 1, if(n even?, collatz(n / 2), collatz(n * 3 + 1)))
)</lang>
Java
<lang java>public class Collatz {
public static void main(String[] args) { for (int x = Integer.parseInt(args[0]); x > 1; x = (x % 2 == 0) ? x / 2 : x * 3 + 1) { System.out.println(x); } }
}</lang>
Oz
<lang oz>declare
fun lazy {CollatzSeq N} N > 0 = true %% assert if N == 1 then [1] elseif {IsEven N} then N|{CollatzSeq N div 2} else N|{CollatzSeq 3*N+1} end end
in
{ForAll {CollatzSeq 42} Show}</lang>
Perl
<lang perl>#!/usr/bin/perl
die("Usage: $0 n\n") if (!$ARGV[0] || !int($ARGV[0]));
my $n = int($ARGV[0]);
while ($n > 1) {
$n = ($n % 2 != 0) ? $n * 3 + 1 : $n / 2; print "$n\n";
} </lang>
PHP
<lang php>while($n > 1) {
if($n % 2 != 0) { $n = $n*3 + 1; } else { $n = $n/2; } echo $n . '
';
}</lang>
PureBasic
<lang PureBasic>While n>1
If n%2 n=(3*n)+1 Else n/2 EndIf PrintN(Str(n))
Wend</lang>
Python
<lang python>def collatz(n):
while n > 1: print (n) if n & 1: n = (n*3)+1 else: n >> 1 print (n)</lang>
Scala
<lang scala>def collatz(n:BigInt):Stream[BigInt] =
if (n == 1) { Stream(1); } else { def next(n:BigInt):BigInt = if ((n % 2) == 0) (n / 2) else (n * 3 + 1); Stream.cons(n, collatz(next(n))); }</lang>
UNIX Shell
<lang sh>collatz () { n=$1; echo $n; if [ "$n" -gt 1 ]; then
#if odd if [ "$(expr $n % 2)" -eq 1 ] ;then collatz $(($n*3+1)) else collatz $(($n/2)) fi
fi }</lang>