Leetcode #1170: Compare Strings by Frequency of the Smallest Character

func numSmallerByFrequency(_ queries: [String], _ words: [String]) -> [Int] {
    var ar = Array(repeating: 0, count: words.count)
    for (i, word) in words.enumerated() {
        ar[i] = frequency(Array(word))
    }
    ar = ar.sorted()
    var answer = Array(repeating: 0, count: queries.count)
    for (i, query) in queries.enumerated() {
        let num = frequency(Array(query))
        answer[i] = binarySearch(ar, num)
    }
    return answer
}

private func frequency(_ str: [Character]) -> Int {
    var smallest = str[0]
    var count = 1
    for i in stride(from: 1, to: str.count, by: 1) {
        if str[i] > smallest {
            continue
        } else if str[i] < smallest {
            smallest = str[i]
            count = 1
        } else {
            count += 1
        }
    }
    return count
}

private func binarySearch(_ ar: [Int], _ num: Int) -> Int {
    var start = 0
    var end = ar.count - 1
    while start <= end {
        let mid = start + (end - start) / 2
        if ar[mid] > num {
            end = mid - 1
        } else {
            start = mid + 1
        }
    }
    return ar.count - start
}