java codility training Genomic-range-query

Question

The task is:

A non-empty zero-indexed string S is given. String S consists of N characters from the set of upper-case English letters A, C, G, T.

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Answer 1

Here is the solution that got 100 out of 100 in codility.com. Please read about prefix sums to understand the solution:

public static int[] solveGenomicRange(String S, int[] P, int[] Q) {
        //used jagged array to hold the prefix sums of each A, C and G genoms
        //we don't need to get prefix sums of T, you will see why.
        int[][] genoms = new int[3][S.length()+1];
        //if the char is found in the index i, then we set it to be 1 else they are 0
        //3 short values are needed for this reason
        short a, c, g;
        for (int i=0; i 0) {
                result[i] = 1;
            } else if (genoms[1][toIndex] - genoms[1][fromIndex] > 0) {
                result[i] = 2;
            } else if (genoms[2][toIndex] - genoms[2][fromIndex] > 0) {
                result[i] = 3;
            } else {
                result[i] = 4;
            }
        }

        return result;
    }