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

My C++ solution

vector solution(string &S, vector &P, vector &Q) {

    vector impactCount_A(S.size()+1, 0);
    vector impactCount_C(S.size()+1, 0);
    vector impactCount_G(S.size()+1, 0);

    int lastTotal_A = 0;
    int lastTotal_C = 0;
    int lastTotal_G = 0;
    for (int i = (signed)S.size()-1; i >= 0; --i) {
        switch(S[i]) {
            case 'A':
                ++lastTotal_A;
                break;
            case 'C':
                ++lastTotal_C;
                break;
            case 'G':
                ++lastTotal_G;
                break;
        };

        impactCount_A[i] = lastTotal_A;
        impactCount_C[i] = lastTotal_C;
        impactCount_G[i] = lastTotal_G;
    }

    vector results(P.size(), 0);

    for (int i = 0; i < P.size(); ++i) {
        int pIndex = P[i];
        int qIndex = Q[i];

        int numA = impactCount_A[pIndex]-impactCount_A[qIndex+1];
        int numC = impactCount_C[pIndex]-impactCount_C[qIndex+1];
        int numG = impactCount_G[pIndex]-impactCount_G[qIndex+1];

        if (numA > 0) {
            results[i] = 1;
        }
        else if (numC > 0) {
            results[i] = 2;
        }
        else if (numG > 0) {
            results[i] = 3;
        }
        else {
            results[i] = 4;
        }
    }

    return results;
}