Question

I have n integers and I need a quick logic test to see that they are all different, and I don’t want to compare every combination to find a match…any ideas on a nice and elegant approach?

I don’t care what programming language your idea is in, I can convert!

Answer 1

You don’t have to check every combination thanks to commutivity and transitivity; you can simply go down the list and check each entry against each entry that comes after it. For example:

bool areElementsUnique( int[] arr ) {
    for( int i=0; i<arr.Length-1; i++ ) {
        for( int j=i+1; j<arr.Length; j++ ) {
            if( arr[i] == arr[j] ) return false;
        }
    }
    return true;
}

Note that the inner loop doesn’t start from the beginning, but from the next element (i+1).