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Thread: Returning the equilibrium index in a sequence of integers

  1. #1
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    Default 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...


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Returning the equilibrium index in a sequence of integers

    Use big integers, or use longs.

  3. #3
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    Default Re: Returning the equilibrium index in a sequence of integers

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

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    Default Re: Returning the equilibrium index in a sequence of integers

    ...
    100%
    Last edited by copeg; September 3rd, 2013 at 02:19 PM. Reason: Removed spoonfeeding

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    Administrator copeg's Avatar
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    Default Re: Returning the equilibrium index in a sequence of integers

    @opastukhov, please don't spoonfeed, especially on a post that is almost 3 years old.

    Thread locked.

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