LeetCode 161. One Edit Distance

LeetCode161.swift

class Solution {
    func isOneEditDistance(_ s: String, _ t: String) -> Bool {
        if (s.count == t.count) {
            return countOfReplaced(s, t) == 1
        }
        
        if (s.count == t.count - 1) {
            return isRemoved(s, t)
        }
        if (t.count == s.count - 1) {
            return isRemoved(t, s)
        }
        
        return false
    }
    
    private func isRemoved(_ shortS: String, _ longS: String) -> Bool {
        for i in 0..<longS.count {
            let newLongS = remove(index: i, from: longS)
            if (newLongS == shortS) {
                return true
            }
        }
        return false
    }
    
    private func countOfReplaced(_ s: String, _ t: String) -> Int {
        var count = 0
        for i in 0..<s.count {
            if (s[i...i] != t[i...i]) {
                count += 1
            }
        }
        return count
    }
    
    private func remove(index: Int, from string: String) -> String {
        var newString = string
        let i = newString.index(newString.startIndex, offsetBy: index)
        newString.remove(at: i)
        return newString
    }
}

extension String {
    
    subscript (bounds: CountableClosedRange<Int>) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[start...end])
    }
    
    subscript (bounds: CountableRange<Int>) -> String {
            let start = index(startIndex, offsetBy: bounds.lowerBound)
            let end = index(startIndex, offsetBy: bounds.upperBound)
            return String(self[start..<end])
        }
}