Ola Krutrim iOS Interview on 17th July 2024

OPTIMAL APPROACH :-
func longestSubstringLength(inputString: String) -> Int {
    guard inputString.count > 0 else { return 0 }

    var longestSubstringLength = 0
    var leftIndex = 0
    var rightIndex = 0
    let inputStringArray = Array(inputString)

    var set = Set<Character>()

    while rightIndex < inputString.count {
        if !set.contains(inputStringArray[rightIndex]) {
            set.insert(inputStringArray[rightIndex])
            rightIndex += 1
            longestSubstringLength = max(longestSubstringLength, rightIndex - leftIndex)
        } else {
            while set.contains(inputStringArray[leftIndex]) {
                set.remove(inputStringArray[leftIndex])
                leftIndex += 1
            }
        }
    }

    return longestSubstringLength
}

BRUTE FORCE APPROACH :-
import Foundation

func longestSubstringLengthBruteForce(inputString: String) -> Int {
    let inputStringArray = Array(inputString)

    for i in 0 ..< inputString.count {
        for j in stride(from: inputString.count - 1, through: i, by: -1) {
            let subString = String(inputStringArray[i ... j])
            print(subString)
            if doesSubstringHaveUniqueChars(inputString: subString) {
              return subString.count
            }
        }
    }

    return 0
}

func doesSubstringHaveUniqueChars(inputString: String) -> Bool {
  let inputStringArray = Array(inputString)
    var set = Set<Character>()

    for i in 0 ..< inputString.count {
      if set.contains(inputStringArray[i]) {
        return false
      }
      set.insert(inputStringArray[i])
    }

    return true
}

print("Longest substring length = \(longestSubstringLengthBruteForce(inputString: "pwwkew"))")