[Codility] Lesson 5 - GenomicRangeQuery

Task discription

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.
  
  

Source code

• S = CAGCCTA 를 예로 들면 accm에는 각 충격 인자의 누적 값인 [0,0,0,0], [0,1,0,0], [1,1,0,0], [1,1,1,0], [1,2,1,0], [1,3,1,0], [1,3,1,1], [2,3,1,1] 이 저장된다.
• 맨 처음의 [0,0,0,0]은 P[i] = 0인 경우를 고려해 넣어준다(안 넣으면 Segmentation Error 발생).
• P[i] = 2, Q[i] = 4는 accm[5]-accm[2] => [0,2,1,0] 이므로 C에 해당하는 최소 충격 계수 2가 답이다.

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

vector<int> ans;

vector<int> solution(string &S, vector<int> &P, vector<int> &Q) {
    vector<int> cnt(4);
    vector<vector<int> > accm;

    fill(cnt.begin(), cnt.end(), 0);
    accm.push_back( {0, 0, 0, 0 }); // P[i] = 0인 경우를 고려해 초기 값 넣어줌.

    // A, C, G, T 의 누적 카운트를 저장
    for(int i=0;i<S.size();i++) {
        if(S[i] == 'A') cnt[0]++;
        else if(S[i] == 'C') cnt[1]++;
        else if(S[i] == 'G') cnt[2]++;
        else cnt[3]++;
        accm.push_back(cnt);
    }

    for(int i=0;i<P.size();i++) {
        for(int j=0;j<4;j++) {
    	    // [0,0,0,0]을 고려해 Q[i]+1 - P[i]
            int num = accm[Q[i]+1][j] - accm[P[i]][j];
            if(num > 0) {
                ans.push_back(j+1);
                break;
            }
        }
    }

    return ans;
}

Review

이중 for문을 통해 풀었더니 성능오류가 발생했다..
결국 구글의 도움을 받았다.. 어려운 문제였다 😥