[Codility] Prefix Sums - GenomicRangeQuery / Java

1. 문제

A DNA sequence can be represented as a string consisting of the letters A, C, G and T, which correspond to the types of successive nucleotides in the sequence. Each nucleotide has an impact factor, which is an integer. Nucleotides of types A, C, G and T have impact factors of 1, 2, 3 and 4, respectively. You are going to answer several queries of the form: What is the minimal impact factor of nucleotides contained in a particular part of the given DNA sequence?

The DNA sequence is given as a non-empty string S = S[0]S[1]...S[N-1] consisting of N characters. There are M queries, which are given in non-empty arrays P and Q, each consisting of M integers. The K-th query (0 ≤ K < M) requires you to find the minimal impact factor of nucleotides contained in the DNA sequence between positions P[K] and Q[K] (inclusive).

For example, consider string S = CAGCCTA and arrays P, Q such that:

P[0] = 2 Q[0] = 4 P[1] = 5 Q[1] = 5 P[2] = 0 Q[2] = 6

The answers to these M = 3 queries are as follows:

• The part of the DNA between positions 2 and 4 contains nucleotides G and C (twice), whose impact factors are 3 and 2 respectively, so the answer is 2.
• The part between positions 5 and 5 contains a single nucleotide T, whose impact factor is 4, so the answer is 4.
• The part between positions 0 and 6 (the whole string) contains all nucleotides, in particular nucleotide A whose impact factor is 1, so the answer is 1.

Write a function:

class Solution { public int[] solution(String S, int[] P, int[] Q); }

that, given a non-empty string S consisting of N characters and two non-empty arrays P and Q consisting of M integers, returns an array consisting of M integers specifying the consecutive answers to all queries.

Result array should be returned as an array of integers.

For example, given the string S = CAGCCTA and arrays P, Q such that:

P[0] = 2 Q[0] = 4 P[1] = 5 Q[1] = 5 P[2] = 0 Q[2] = 6

the function should return the values [2, 4, 1], as explained above.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [1..100,000];
• M is an integer within the range [1..50,000];
• each element of arrays P, Q is an integer within the range [0..N − 1];
• P[K] ≤ Q[K], where 0 ≤ K < M;
• string S consists only of upper-case English letters A, C, G, T.

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2. 코드

class Solution {
    public int[] solution(String S, int[] P, int[] Q) {

        int[] result = new int[P.length];
        
        int[] A = new int[S.length()+1];
        int[] C = new int[S.length()+1];
        int[] G = new int[S.length()+1];
        int[] T = new int[S.length()+1];
        
        for(int i=0; i<S.length(); i++) {
            char c = S.charAt(i);
            if(c == 'A')
                A[i+1]++;
            else if(c == 'C')
                C[i+1]++;
            else if(c == 'G')
                G[i+1]++;
            else if(c == 'T')
                T[i+1]++;
            
            A[i+1] += A[i];
            C[i+1] += C[i];
            G[i+1] += G[i];
            T[i+1] += T[i];
            
        }

        for(int i=0; i<P.length; i++) {
            int start = P[i];
            int end = Q[i];
            
            if(end - start == 0) {
                char c = S.charAt(start);
                
                if(c == 'A')
                    result[i] = 1;
                else if(c == 'C')
                    result[i] = 2;
                else if(c == 'G')
                    result[i] = 3;
                else if(c == 'T')
                    result[i] = 4;
            }
            else if(A[start] != A[end+1])
                result[i] = 1;
            else if(C[start] != C[end+1])
                result[i] = 2;
            else if(G[start] != G[end+1])
                result[i] = 3;
            else if(T[start] != T[end+1])
                result[i] = 4;
        }
        
        return result;
    }
}