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

I think I'm using dynamic programming. Here is my solution. Little space. Code is mot really clean, just show my idea.

class Solution {
public int[] solution(String S, int[] P, int[] Q) {
    int[] preDominator = new int[S.length()];
    int A = -1;
    int C = -1;
    int G = -1;
    int T = -1;

    for (int i = 0; i < S.length(); i++) {
        char c = S.charAt(i);
        if (c == 'A') { 
            A = i;
            preDominator[i] = -1;
        } else if (c == 'C') {
            C = i;
            preDominator[i] = A;
        } else if (c == 'G') {
            G = i;
            preDominator[i] = Math.max(A, C);
        } else {
            T = i;
            preDominator[i] = Math.max(Math.max(A, C), G);
        }
    }

    int N = preDominator.length;
    int M = Q.length;
    int[] result = new int[M];
    for (int i = 0; i < M; i++) {
        int p = P[i];
        int q = Math.min(N, Q[i]);
        for (int j = q;;) {
            if (preDominator[j] < p) {
                char c = S.charAt(j);
                if (c == 'A') {
                    result[i] = 1;
                } else if (c == 'C') {
                    result[i] = 2;
                } else if (c == 'G') {
                    result[i] = 3;
                } else {
                    result[i] = 4;
                }
                break;
            }
            j = preDominator[j];
        }
    }
    return result;
}

}