import UIKit
​
var str = "abcabcaaa"
var count = [String: Int]()
​
for char in str {
  let c = String(char)

  if count[c] != nil {
    count[c] = count[c]! + 1
  } else {
    count[c] = 1
  }
//  if let tempCount = count[c] {
//    tempCount[c] = tempCount[c]! + 1
//  } else {
//    tempCount[c] = 1
//  }

}
​
let sortedKeys = (count as NSDictionary).keysSortedByValue(using: #selector(NSNumber.compare(_:)))
let key = sortedKeys.last! as! String
print(key)
print(count[key]!)