Swift: Most frequently occurring character in a string

Frequency.swift

// I publicly share any answers to "coding challenges" I receive as a part of the interview process
// copy/paste this into an Xcode playground or the code challenge repl of choice

// Write a function in Swift that takes in a string as input and returns the most frequently occurring character in the string.
// If multiple characters have the same highest frequency, return any one of them.

func frequency(_ input: String) -> Character {
    let charFrequency = input.reduce(into: [:]) {counts, char in
        counts[char, default: 0] += 1
    }
    let maxFrequency = charFrequency.values.max()
    
    let mostFrequentChars = charFrequency.filter {$0.value == maxFrequency}
    
    return mostFrequentChars.keys.first ?? Character("0")
}

print(frequency("testorama"))
// a