CODEWITHSUNDEEP
java
phoenix
phoenix

Reputation: 3621

random number generation and exclusion of the generated numbers


Is it possible to do this in Java ? I want to generate a random number such that given a range say for example: between 1 and 70 - everytime the random number is generated it should be excluded from generation results.
so [1,70] rand = 56 (now 56 shouldn't be considered next time)
[1,70] = 63 (now 56,63 should be excluded from generation till my code runs)

Upvotes: 0

Views: 1514

Answers (4)

kensen john
kensen john

Reputation: 5519

Another trivial alternative, using HashMaps to keep track of random numbers. It is sort of quick and dirty.

HashMap<Integer,Integer> hmRandomNum = new HashMap<Integer,Integer>();

Integer a = < generate random number>

if( hmRandomNum.get(a) == null)
{
     hmRandomNum.put(a,a);
}
else
{
     // ignore this random number. this was already selected and present in the hashmap.
}

//Iterate depending on how many numbers you want.

Upvotes: 1

A D
A D

Reputation: 809

you could populate the range into an array and shuffle the array. This would be inefficient though for very large ranges

Upvotes: 1

Pete
Pete

Reputation: 10871

I asked the same question here: How can I generate a random number within a range but exclude some?

The general strategy is something like filling an array with 70 values. Just remove the values that you randomly generate as per the link above.

Upvotes: 1

Jim Garrison
Jim Garrison

Reputation: 86774

This is equivalent to shuffling an array of numbers containing [1..70] and then dealing them out one at a time. Look up "shuffle algorithm" on Google. Here's a link http://www.vogella.de/articles/JavaAlgorithmsShuffle/article.html

Upvotes: 3

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