How to produce a unique number from combination of 2 numbers (in any order) in PHP?

Question

How to produce a unique number from combination of 2 numbers in PHP ? For example, combination of these two numbers; 68 and 73, produce X ( X is a unique number). It does not matter how the order of the combination numbers, it should still produce same unique number. E.g: (68,73)=X or (73,68)=X or combination of (1,2)=Y or (2,1)=Y , Y is a different number (because it's unique) from X.

Let me know if you need more information.

I think this problem is similar to my problem but it is written in C#.

I converted this code to PHP :

function getUnique($x, $y){
  if($x>$y){
    return $y | $x << 32;
  }  else{
    return $x | $y << 32;
  }
}

$list = array();
for($i=0 ; $i<100 ;$i++){
  $x = rand(1,10); // I just put any random numbers from 1 to 10 so that I can read it easily.
  $y = rand(1,10);
  $unique = getUnique($x, $y);
  $list[$i] = '('.$x.','.$y.')='.$unique;
 }

//Find out the results
foreach($list as $ans){
   echo $ans.'<br>';
}

But, it does not produce unique numbers. Example from this results:

(2,9)=11

(10,1)=11

(2,9) should produce different number from (10,1).

Is there a maximum for the input numbers (for example 100)? Such that you would never get (37,205). If not, no. If yes, then absolutely. — jedwards, May 20 '12 at 02:57
are you looking for the value of X and Y. like 12+24= **36** and any combination of numbers that sum **36** your question is confusing. — Lawrence Cherone, May 20 '12 at 03:11
Then no, it is not possible. It would be possible if you specified a maximum input, otherwise unfortunately no. — jedwards, May 20 '12 at 03:45
This question seems legit. What's the reason to close? Anyway I have added a new answer in the same SO thread you posted which addresses your concern. Or see this link http://stackoverflow.com/a/13871379/661933 — nawfal, Dec 14 '12 at 14:05

Oliver Charlesworth · Answer 1 · 2012-05-20T03:10:21.107

2

No, at least not in general (though there may be if you specify some restrictions).

Assuming n-bit types, there are 2ⁿ possible values. But there are 2²ⁿ possible pairs of values. Obviously there's not a unique mapping from a pair to a value.

Of course, if you're prepared to have an output type that's wider than your input type, then this is trivial.

edited May 20 '12 at 03:10

answered May 20 '12 at 03:03

Oliver Charlesworth

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I don't think you understood the question. In fact there is a way to produce what he is looking for if there is a maximum input. – jedwards May 20 '12 at 03:07
@jedwards: So what do you interpret the question to mean? – Oliver Charlesworth May 20 '12 at 03:07
Write a function that, given a set of numbers `(a,b)` produce a number `x` such that: `(b,a)` also produces `x` and no other `(a',b')` pair produces `x`. – jedwards May 20 '12 at 03:09
@jedwards: Yes, that was my understanding too. – Oliver Charlesworth May 20 '12 at 03:10
If the maximum input was 9, then sorting the numbers and concatenating them would do exactly what he wants. (2,4) = 24 = (4,2). No other acceptable `(a,b)` pair would result in 24. – jedwards May 20 '12 at 03:12
+1 Oli is right you can't map 2 numbers to 1 unique number with a domain of -inf to inf – None May 20 '12 at 03:12
@jedwards: Yes, **if** there's such a restriction, then I agree. Given no restriction, then there is no solution (which is what my answer says). – Oliver Charlesworth May 20 '12 at 03:13
Which is what your answer says now, I agree, however originally you didn't have such a qualification. Hence my comment. Downvote revoked. – jedwards May 20 '12 at 03:13
An edit or comment would have done instead of -1. – None May 20 '12 at 03:14
The answer was originally an unhelpful "No." followed by some justification. When in fact, the answer is more complex as I indicated in my comment to the original question. – jedwards May 20 '12 at 03:16
@jedwards: My answer was "no..." because the OP has currently specified no constraints. – Oliver Charlesworth May 20 '12 at 03:18

How to produce a unique number from combination of 2 numbers (in any order) in PHP?

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