Thread: Returning the equilibrium index in a sequence of integers

Hi guys.

I'm new to the forum. I was playing with an online Java test from codility about a function that returns the equilibrium index in a sequence of integers (Codility). The problem states:

Equilibrium index of a sequence is an index such that the sum of elements at lower indexes is equal to the sum of elements at higher indexes. For example, in a sequence A:

A[0]=-7 A[1]=1 A[2]=5 A[3]=2 A[4]=-4 A[5]=3 A[6]=0
3 is an equilibrium index, because:

A[0]+A[1]+A[2]=A[4]+A[5]+A[6]
6 is also an equilibrium index, because:

A[0]+A[1]+A[2]+A[3]+A[4]+A[5]=0
(sum of zero elements is zero) 7 is not an equilibrium index, because it is not a valid index of sequence A.

[...]

Assume the sum of zero elements is equal zero. Write a function
int equi(int[] A);
that given a sequence, returns its equilibrium index (any) or -1 if no equilibrium indexes exist. Assume that the sequence may be very long.

My solution to this was the following:

int equi ( int[] A ) {        
 
    int leftSum = 0;
    int rightSum = 0;
 
    for (int iterator= 0; iterator< A.length; iterator++){
        rightSum += A[iterator];
    }
 
    for(int eqIndexCandidate = 0; 
        eqIndexCandidate < A.length;
        eqIndexCandidate ++){
 
        if (eqIndexCandidate != 0)
           leftSum += A[eqIndexCandidate - 1];
 
        rightSum -= A[eqIndexCandidate];
 
        if (leftSum == rightSum)
            return eqIndexCandidate;
 
    }
 
    return -1;
}

However, when I got the results back it seems that I missed one case:



How would you deal with a case that the numbers are too large to fit in an integer ? It seems that Codility would not let me use any packages from the API...

large numbers - check for Integer.MAX_VALUE and MIN_VALUE before summing the stuff. I got 100% there.