Limit input data to achieve a better Big O complexity

Question

You are given an unsorted array of n integers, and you would like to find if there are any duplicates in the array (i.e. any integer appearing more than once). D

Answer 1

A variance of Bucket Sort will do. This will give you complexity of O(n) where 'n' is the number of input elements.

But one restriction - max value. You should know the max value your integer array can take. Lets say it as m.

The idea is to create a bool array of size m (all initialized to false). Then iterate over your array. As you find an element, set bucket[m] to true. If it is already true then you've encountered a duplicate.

A java code,

// alternatively, you can iterate over the array to find the maxVal which again is O(n).
public boolean findDup(int [] arr, int maxVal)
{
        // java by default assigns false to all the values.
    boolean bucket[] = new boolean[maxVal];

    for (int elem : arr)
    {

        if (bucket[elem])
        {
           return true; // a duplicate found
        }

        bucket[elem] = true;
    }   
    return false;   
}

But the constraint here is the space. You need O(maxVal) space.