# [Codility] Prefix Sums - GenomicRangeQuery 풀이

# 예문

https://app.codility.com/programmers/lessons/5-prefix_sums/genomic_range_query/

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.
```

## 해석

- DNA sequence : 문자 A,C,G,T로 구성된 문자열 S
- S : N개의 문자로 구성된 비어 있지 않은 문자열 S[0]S[1]..S[N-1]
- A,C,G,T는 각각 1,2,3,4 이라는 impact factor 로 매치됨.
- 배열 P, Q : 비어있지 않은 배열로 각각 M개의 정수로 구성 됨
- K번째 query : (0 <= K < M) 위치 P[K]와 Q[K] 사이의 DNA sequence 포함된 최소 impact factor를 찾음.
- 주어진 DNA sequence의 K번째 query 들로 이루어진 배열을 리턴하라!

## 풀이

- 각 글자별 누적 카운트를 저장
- 누적카운트[endIndex] - 누적카운트[startIndex - 1] 를 계산

## 제약사항

- N의 범위는 정수 [1..100,000]
- M의 범위는 정수 [1..50,000]
- P,Q 배열의 각 요소의 범위는 정수 [0..N - 1]
- P[K] <= Q[K]
- 0 <= K < M
- S : 대문자 A,C,G,T 으로만 구성됨

## 코드

```
public int[] solution(String S, int[] P, int[] Q) {
int length = S.length();
int impactLength = 4;
int[] impactCnt = new int[impactLength];
int[][] impactFactorArray = new int[impactLength][length + 1];
char c;
int impactFactor = 0;
for (int i = 0; i < length; i++) {
c = S.charAt(i);
if ('A' == c) impactFactor = 1;
else if ('C' == c) impactFactor = 2;
else if ('G' == c) impactFactor = 3;
else if ('T' == c) impactFactor = 4;
impactCnt[impactFactor - 1] += 1;
for (int j = 0; j < impactLength; j++) {
impactFactorArray[j][i + 1] = impactCnt[j];
}
}
int[] result = new int[P.length];
for (int i = 0; i < P.length; i++) {
for (int j = 0; j < impactLength; j++) {
if (impactFactorArray[j][Q[i] + 1] - impactFactorArray[j][P[i]] > 0) {
result[i] = j + 1;
break;
}
}
}
return result;
}
```