Find duplicates in an array using javascript

Problem :

Given an array of positive integers find all the duplicate elements.

Algorithm :

  • Iterate over the array using forEach
    • Find if there is a duplicate for the element using indexOf
    • indexOf takes two arguments first the element and the second one is the starting index
    • We provide the starting index as the index + 1 where index is the index of the current element
    • We will find if the same element exists on the right hand side of that element or not

    • If there’s a duplicate and the element is not already being added to the result then push it to the array.

Solution :

Further reading :

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1 Response

  1. Alan Mimms says:

    Sorry, but this algorithm is not O(1). It’s also not O(n).

    It is actually O(n^2). The data.indexOf call in the loop effectively makes the comparisons done be proportional to data.length * data.length = n^2.

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