Javascript random values that add to a certain number

Question

I have an array of numbers that can range from zero to infinity. I need to generate random numbers lower than that of the numbers in the array, one for each number. For example if i have the numbers:

[10, 5, 0, 7]

An output could be any of:

[5, 3, 0, 6] or [1, 0, 0, 7] or [10, 5, 0, 7]

This is simple enough, but my problem lies with the next part. I have to make sure these numbers add up to a specified value. For example, the same first array could produce:

[4, 3, 0, 1] or [8, 0, 0, 0]

with the total value being 8.

After doing some research, i found this post but sadly, it does not incorporate per-value limits. Rather it has one total, and generates a set of numbers according to that. I need all of these numbers to be less an that of an inputted array. Using Jquery's each loop, you can create a vale less than that of the number corresponding, but how would i incorporate the total value?

If someone could modify that post to have a three values, being total, max, and min, it would be very appreciated. At this point, i am clueless.

This sounds like homework. Post your attempt at a solution and we'd be glad to look at it. — colonelsanders
– colonelsanders, Commented Oct 15, 2014 at 22:20

EvilZebra · Accepted Answer · 2014-10-15 22:38:10Z

2

Here is a basic solution. Note that I set maxLoops or else this function could potentially run forever.

function randomize(array, total){
    var maxLoops = 100, randomized;
    do{
        randomized = array.map(function(value){
           return Math.floor(Math.random()*(value+1)); 
        });
        maxLoops--;
    }while(maxLoops > 0 && randomized.reduce(function(a, b){ return a+b; }) !== total);

    return randomized;
}

var test = randomize([10, 5, 0, 7], 8);
console.log(test);

http://jsfiddle.net/fx7a1w28/

answered Oct 15, 2014 at 22:38

EvilZebra

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4 Comments

btm1 Over a year ago

if I change the array going in to anything other than the one provided and change the total this no longer works

EvilZebra Over a year ago

Hmm I just tested my code again and it seems to work just fine. What did you enter as array and total?

Brad Adams Over a year ago

This works great! However when I tried using this to create a total number that had a decimal, the result always equaled the rounded value. Any ideas?

EvilZebra Over a year ago

Certainly, note on the 5th line of my example I am using Math.floor(), this causes all values to always be a whole number. The code would need to be changed a bit to support decimal values.

Weather Vane · Accepted Answer · 2014-10-16 21:52:02Z

1

I solved this in a single pass, by constraining the limits of each digit.

<html><body><script language="javascript">
var arry = [10, 5, 0, 7];
var ansa = [];
var required = 8;
var sum = 0;
for (i=0; i<arry.length; i++) {
    max = required - sum;
    if (max > arry [i])
        max = arry [i];
    min = required - sum;
    for (j=i+1; j<arry.length; j++)
        min = min - arry [j];
    if (min < 0) min = 0;
    if (min > max) {
        ansa [i] = 'Impossible';
        break;
        }
    num = min + Math.floor (Math.random () * (max - min + 1));
    ansa [i] = num;
    sum = sum + num;
    }
document.writeln (ansa);
</script></body></html>

answered Oct 16, 2014 at 21:52

Weather Vane

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Comments

Encinoman818 · Accepted Answer · 2014-10-16 19:02:49Z

I will give you the steps. It's quite simple.

First create a function which takes an array of numbers as an argument and generates an array of random numbers less than or equal to every element of the input array. Return an associative array with the first key mapping to the sum you desire and the second key mapping to the randomly generated array.

Second create a do while loop which continues to call the function until the first key is equal to the sum of the elements you desire. The solution will then be the second key.

function generateRandomArray(input){

output = [];
for(i = 0; i <input.length; i++){ 
      output.push(Math.floor((Math.random() * input[i]) + 1))
     }

      output_sum = 0
      for(i=0; i < output.length; i++){
      output_sum += output[i]   
     }

    return {'output_sum':output_sum, 'output_array':output}

}

desired sum = 8
example_input = [10, 5, 0, 7]
do {test_output = generateRandomArray(example_input)['output_sum']} while 
(test_output != desired_sum)

correct_array = test_output['output_array]

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