Generate same random number based on string parameter-CodePudding

I'm trying to create a function that will generate the same random number on each execution if the string is the same.

function generateRandom(maxInt, stringParam) {
  //generate random based on stringParam
  //output int number from 0 to maxInt
}

The goal is to generate the same random number (on different pages) if the stringKey is the same.

generateRandom(100, 'abc') // 73
generateRandom(100, 'abc') // 73
generateRandom(100, 'abc') // 73

generateRandom(100, 'qwe') // 45
generateRandom(100, 'qwe') // 45
generateRandom(100, 'qwe') // 45

CodePudding user response：

This isn't really random. I would say this is a kind of encryption. Hopefully, it works for your requirement.

First, get the Unicode from each character in the string. Sum them up and then use % (Remainer operator) to round the number to be within MaxInt range. This will result in the same number every time you input the same maxInt and the same stringParam.

function generateRandom(maxInt, stringParam) {
  let sum = 0;
  for (let i = 0; i < stringParam.length; i  ){
    sum  = stringParam.charCodeAt(i);
  }
  let result = sum % maxInt;
  console.log(result);
  return result;
}

generateRandom(100, 'abc')
generateRandom(100, 'abc')
generateRandom(100, 'abc')

generateRandom(100, 'qwe')
generateRandom(100, 'qwe')
generateRandom(100, 'qwe')

CodePudding user response：

I'd suggest using a hashing function for this purpose, perhaps a simple one in this case.

Once we have the hash we'll mod with our max output value, e.g. hash % maxInt.

This will give the same output for a given input.

// Simple implementation of a string hashing function (Bernstein)
function hashCode(input) {
    return [...input].reduce((hash, chr) => { 
        return hash * 33   chr.charCodeAt(0);
    }, 0);
}

function generateRandom(maxInt, stringParam) {
    return hashCode(stringParam) % maxInt;
}

const maxInt = 100;
const inputs = [ 'qwe', 'qwe', 'abc', 'abc', 'def', 'def'];

console.log('In ', 'Out')
inputs.forEach(input => console.log(input, generateRandom(maxInt, input)));

.as-console-wrapper { max-height: 100% !important; }