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

   static public int[] solution(String S, int[] P, int[] Q) {
    // write your code in Java SE 8

    int A[] = new int[S.length() + 1], C[] = new int[S.length() + 1], G[] = new int[S.length() + 1];

    int last_a = 0, last_c = 0, last_g = 0;

    int results[] = new int[P.length];
    int p = 0, q = 0;
    for (int i = S.length() - 1; i >= 0; i -= 1) {
        switch (S.charAt(i)) {
            case 'A': {
                last_a += 1;
                break;
            }
            case 'C': {
                last_c += 1;
                break;
            }

            case 'G': {
                last_g += 1;
                break;
            }

        }
        A[i] = last_a;
        G[i] = last_g;
        C[i] = last_c;
    }


    for (int i = 0; i < P.length; i++) {
        p = P[i];
        q = Q[i];

        if (A[p] - A[q + 1] > 0) {
            results[i] = 1;
        } else if (C[p] - C[q + 1] > 0) {
            results[i] = 2;
        } else if (G[p] - G[q + 1] > 0) {
            results[i] = 3;
        } else {
            results[i] = 4;
        }

    }
    return results;
}