In my (Java Android) game, I spawn coins at random positions.
Coins can appear at one of 6 positions horizontally across the screen (2 max per horizontal level).
What I do is create a random number between 0 and 5 for the first coin, then I want generate another random number excluding the position of the first coin.
So, for example, coin 1 is spawned at a random position between 0 and 5 - so let's say 4.
Then the next coin needs to be able to choose between 0-3 or 5. (basically 0-5 excluding 4).
I have managed to do it, but it's not very elegant and I'm sure there must be a better/cleaner way to achieve this, however, it escapes me.
The random(int number) method in the code below simply returns a random int from 0 to number-1 (uses nextInt) and randomBool() just returns a random boolean
Also, please bear in mind that I don't want to use any technique that keeps re-generating a random number if the one it produces is equal to the one we are trying to avoid.
code
//Return a random number between 0 and 5 excluding the specified number
private int getRandomExcluding(int excludedNumber){
//If previous position was 0 then generate a number between 1 and 5
if (excludedNumber==0){
return random(5)+1;
}
//If position was 5, then generate and return number from 0-4
else if (excludedNumber==5){
return random(5);
}
//If number isn't 0 or 5 (then it is in range of 1-4 use a random bool to determine
// if we are going to get a number less than or greater than the number we are excluding
//True - get number lower than excluded number
else if(randomBool()){
//Excluded number is 1
if (excludedNumber==1){
return 0; //Only posibility
}
//Excluded number is > 1
else {
//Return a random number between 0 (inclusive) and the excluded number (exclusive)
return random(excludedNumber);
}
//False - get number higher than the excluded number (between exludedNumber+1 (inclusive) and 6(exlusive))
else {
return random(6-(excludedNumber+1))+(excludedNumber+1);
}
}
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