Palindrome Permutation.swift

import Foundation
import XCTest

func isPermutationOfPalindrome(_ string: String) -> Bool {
  let characterCounts: [Character: Int] = string.reduce(into: [:], { (dict, character) in
    dict[character] = (dict[character] == nil) ? 1 : (dict[character] ?? 0) + 1
  })

  // Do I really need to do this? 🤔
  let keys = Array(characterCounts.keys)
  let firstIndex = keys.firstIndex { (characterCounts[$0] ?? 0) % 2 != 0 }

  guard let nonNullFirstIndex = firstIndex else {
    return true
  }

  if nonNullFirstIndex == keys.endIndex {
    return true
  }

  let secondIndex = keys[(nonNullFirstIndex + 1)...].firstIndex { (characterCounts[$0] ?? 0) % 2 != 0 }
  return secondIndex == nil
}


class PalindromeTests: XCTestCase {

  let words: [String: Bool] = [
    "abuttuba": true,
    "acaramanamaraca": true,
    "aladnamedemandala": true,
    "asdfghj": false,
    "hannah": true,
    "civic": true,
    "racecar": true,
    "anahhn": true
  ]

  func testWithLotsOfWords() {
    for (key, value) in words {
      print("Testing for \(key)")
      print("result is \(isPermutationOfPalindrome(key))")
      XCTAssertEqual(isPermutationOfPalindrome(key), value)
    }
  }
}

PalindromeTests.defaultTestSuite.run()