Generate random number that doesn't previously exist in a list-CodePudding

How can I create a random 16 digit number that doesn't previously exist in a list?

Let's say I have the following list:

const nums = [7856328870763265, 0107654389657487];

I need a function to generate random 16 digit numbers but that doesn't create duplicates.

I have the following:

const val = Math.floor(1000   Math.random() * 9000).toString();
const random16digitnumber =  val val val val;
console.log(random16digitnumber);  
console.log(typeof random16digitnumber);

But im afraid at some point it will start creating duplicates. I'm using the random16digitnumber as a primary key in a SQL database for a small school project.

So going back to my example, how can I create a random 16 digit number that doesn't previously exist in an array?

CodePudding user response：

I'll answer with an inline comment. I left your algo "as is". There might be reasons of why you're doing it this way; so I just implemented the logic you've wished for.

const nums = [7856328870763265, 0107654389657487];

const getNextRandomNumber = () => {
    const val = Math.floor(1000   Math.random() * 9000).toString();
    const candidate =  val val val val;

    // the generated number is part of the list; 
    // recursively call this function to generate another one
    // (this works like a loop, just using call recursion)
    // until a number is found that is not part of the list
    // then the return below this if() is triggered
    // and the "good" candidate is returned
    if (nums[candidate]) {
        return getNextRandomNumber();
    }
    // parseInt makes sure the string is converted back to number
    // making sure we're using base 10, even if the first digit 
    // might be 0
    return parseInt(candidate, 10);
}

// push() adds an element to the array
// the return value (100% guaranteed to be collision free random number)
// is added via the function call. The function logic makes sure
// it is absolutely unique
nums.push(getNextRandomNumber());