Swift 练笔 —— 统计元音字母

/***********************************************************
@Execise: 
    统计元音字母：
        计算一段字符串中元音字母出现的频次
@notice:
    1. 网上有看到各种实现方式，有用元组记录的，但个人觉得字典最简洁
***********************************************************/

// 元音字母集合
let vowels: Set<Character> = ["A", "E", "I", "O", "U"]

// 获取元音字母出现的频次
func getVowelNum(_ string: String) -> [String:Int] {
    var dict: [String:Int] = ["A":0, "E":0, "I":0, "O":0, "U":0]
    for c in string.characters {
        let s = String(c).uppercased()
        if dict[s] != nil {
            dict[s]! += 1
        }
    }
    return dict
}

// 测试
print(getVowelNum("The goals of an NPO are always to change or improve a social issue."))
print(getVowelNum("IEEE stands for the 'Institute of Electrical and Electronics Engineers'."))

// 输出
// ["O": 7, "A": 8, "I": 3, "U": 1, "E": 5]
// ["O": 3, "A": 3, "I": 6, "U": 1, "E": 12]