Find the Duplicate Number

Ashwin — Thu, 13 Aug 2020 15:09:28 +0000

I was given a challenge by a friend to find the duplicates in an array.

For instance, a function when it receives an array -

[1, 2, 3, 4, 5, 2, 2, 2]

should return the duplicated number 2

He challenged me to write the code without using more than 1 loop.

My first try

const findDuplicate = nums => {

    const uniqueSet = []
    let duplicate = null
    nums.map(x => {
        if(uniqueSet.includes(x)){
           duplicate = x 
        }
        uniqueSet.push(x)
    })
    return duplicate
}

so, findDuplicate([1, 2, 3, 4, 5, 2, 2, 2]) returns 2

He was not satisfied but wanted to try differently rather than looping it through.

After hours of breaking my head, I came up with this -

const findDuplicate = nums => {

    const uniqueSet = new Set(nums)
    const arrSum = nums.reduce((a, b) => a + b)

    let uniqueArray = Array.from(uniqueSet)
    const uniqueSetSum = uniqueArray.reduce((a, b) => a + b)
    const duplicate = Math.abs(arrSum - uniqueSetSum) / (nums.length - uniqueArray.length)

    return duplicate
}

He did not understand what is going on at the first look. After a while, he understood the code.

Which one do you prefer? Simpler code or Complex code? Or is there any other way you would solve this?

Share your thoughts. Thanks.

DEV Community: Ashwin

Find the Duplicate Number