how can I make a random array, that has a random value which occurs only once per array

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ceeszz

how can I make a random array, that has a random value which occurs only once per array

in Programming Questions • 1 year ago

how can I make a random array, that has a random value which occurs only once per array.

int[] randomarray = new int[18];

int check;

for (int i = 0; i<18; i++) {

check=0;

randomarray[i] = int(random(0, 20));

while (check<18) {

if (randomarray[i] == randomarray[check]) {

randomarray[i] = int(random(0, 20));

check=0;

}

else {

check++;

}

thanks in advance! :)

Replies(4)

v.k.

Re: how can I make a random array, that has a random value which occurs only once per array

1 year ago

One wat to do it, would be fill the array sequentially. shuffle. and access in regular order.

123456789

shuffle

938416527

use

ceeszz

Re: Re: how can I make a random array, that has a random value which occurs only once per array

1 year ago

thx mate it works:

int[] randomarray = new int[18];

for(int t=0; t<randomarray.length; t++){

randomarray[t]=t;

}

for (int k=0; k < randomarray.length; k++) {

// Goal: swap the value at pos k with a rnd value at pos x.

// save current value from pos/index k into temp

int temp = randomarray[k];

// make rnd index x

int x = (int)random(0, randomarray.length);

// overwrite value at current pos k with value at rnd index x

randomarray[k]=randomarray[x];

// finish swapping by giving the old value at pos k to the

// pos x.

randomarray[x]=temp;

}

println(randomarray);

v.k.

Re: how can I make a random array, that has a random value which occurs only once per array

1 year ago

Cool, your own shuffle! In this post benja has showed a built in shuffle function in Java. And there is a very known shuffle method called Fysher-Yates shuffle with some code examples in wikipedia. I've made this try of implementation of their algorithm some time ago.

void shuffle(int[] array) {

// i is the number of items remaining to be shuffled.

for (int i = array.length; i > 1; i--) {

// Pick a random element to swap with the i-th element.

int j = rng.nextInt(i); // 0 <= j <= i-1 (0-based array)

// Swap array elements.

int tmp = array[j];

array[j] = array[i-1];

array[i-1] = tmp;

}

not_55

Re: how can I make a random array, that has a random value which occurs only once per array

1 year ago

I've done this many time in the past by having an initial string, say "ABCDEFGH", choosing a random position within it's current length then reconstructing the string by 'removing' the characternumber, so....

r=random(length of string)
if r=5 the fifth value would be used 'E', the string would become ABCDFGH and length would become one less for the next pass until length=0.

Not sure how that compares with your shuffling performance wise but it always seemed pretty economical to me? :)

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