Palindrome work in progress.swift

let test = "abba"

class Solution {
    func expandPalindrome(input: String, startIndex: Int, endIndex: Int) -> (Int, Int) {
        var start = startIndex
        var end = endIndex
        let inputArray = Array(input)
        var result = (start, end)
        
        repeat {
            result = (start, end)
            
            start -= 1
            end += 1
            
        } while start >= 0 && end < input.count && inputArray[start] == inputArray[end]
        
        return result
    }
    
    func countSubstrings(_ s: String) -> String {
        
        var output = ""
        let arrs = Array(s)
        
        s.enumerated().forEach { index, character in
            let (start, end) = expandPalindrome(input: s, startIndex: index, endIndex: index)
            
            if end - start + 1 > output.count {
                output = String(arrs[start...end])
            }
        }
        
        for (index, character) in arrs.enumerated() {
            guard String(character) == String(arrs[index + 1]) else { continue }
            
            let (start, end) = expandPalindrome(input: s, startIndex: index, endIndex: index)
            
            if end - start + 1 > output.count {
                output = String(arrs[start...end])
            }
        }
        
        return output
    }
}

Solution().countSubstrings(test)