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

This is a Swift 4 solution to the same problem. It is based on @codebusta's solution above:

public func solution(_ S : inout String, _ P : inout [Int], _ Q : inout [Int]) -> [Int] {
var impacts = [Int]()
var prefixSum = [[Int]]()
for _ in 0..<3 {
    let array = Array(repeating: 0, count: S.count + 1)
    prefixSum.append(array)
}

for (index, character) in S.enumerated() {
    var a = 0
    var c = 0
    var g = 0

    switch character {
    case "A":
        a = 1

    case "C":
        c = 1

    case "G":
        g = 1

    default:
        break
    }

    prefixSum[0][index + 1] = prefixSum[0][index] + a
    prefixSum[1][index + 1] = prefixSum[1][index] + c
    prefixSum[2][index + 1] = prefixSum[2][index] + g
}

for tuple in zip(P, Q) {
    if  prefixSum[0][tuple.1 + 1] - prefixSum[0][tuple.0] > 0 {
        impacts.append(1)
    }
    else if prefixSum[1][tuple.1 + 1] - prefixSum[1][tuple.0] > 0 {
        impacts.append(2)
    }
    else if prefixSum[2][tuple.1 + 1] - prefixSum[2][tuple.0] > 0 {
        impacts.append(3)
    }
    else {
        impacts.append(4)
    }
}

   return impacts
 }