I've been learning C# for a few months now, and I've done some basic things in java last year. I made a solution for the problem the title states, this is the task description.

Task description

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.

This is my 100% task score solution in C#. What things can be improved?

/// <summary>
/// Find the minimum impact factor for every query in a given chain
/// </summary>
/// <returns>
/// An array of ints, every int represents the minimum impact factor found 
/// within ranges in a given chain
/// </returns>
public int[] GetMinimumImpactFactors(string S, int[] P, int[] Q)
    //nuc(s) is short for nucleotide(s)
    Dictionary<char, int> nucsDict = new Dictionary<char, int>(){{'A',1},{'C',2},{'G',3},{'T',4}};
    int[] result = new int[P.Length];
    int[] nucsInOrder= new int[S.Length];
    int nucsIndex = 0;
    //iterate through dictionary, looking for A's, then C's, and so on...
    foreach ( var searchedImpactPair in nucsDict )
        //Appearances of <searchedImpactPair.Key> have a given position in <S> chain, those positions are saved
        for (int currNucPos=0; currNucPos < S.Length; currNucPos++ )
            if( S[currNucPos] == searchedImpactPair.Key )
                nucsInOrder[nucsIndex++] = currNucPos ;
    int start, end, minImpactValueFound, minNucFound;
    char nucleotide;
    for(int positionWithinRange = 0; positionWithinRange < P.Length; positionWithinRange++)

        start = P[positionWithinRange];
        end = Q[positionWithinRange];
        for ( int nucInOrder = 0; nucInOrder < nucsInOrder.Length; nucInOrder++ )
            minNucFound = nucsInOrder[nucInOrder];
            if ( minNucFound >= start && nucsInOrder[nucInOrder] <= end)
                nucleotide = S[minNucFound];
                minImpactValueFound = nucsDict[nucleotide];
                result[positionWithinRange] = minImpactValueFound;
    return result;

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