Finding the most common character in a string. Swift implementation.

gistfile1.swift

import UIKit

var str = "aaaabbbaaaa * bbbb b bbbbbbb ccccccccdd ddddddd dddd"
var cnt = [String: Int]()
var i = 0

for char in str {
    var c = String(char)
    
    if let match = cnt[c] {
        cnt[c] = cnt[c]!+1
    } else {
        cnt[c] = 1
    }
    i++
}

let sortedKeys = (cnt as NSDictionary).keysSortedByValueUsingSelector("compare:")
let key = sortedKeys.last! as NSString

println(key)
// Returns "B"