929. 独特的电子邮件地址

func numUniqueEmails(emails []string) int {
    m := make(map[string]int)
    for _, email := range emails {
        result := strings.Split(email, "@")
        before := result[0]
        after := result[1]
        result = strings.Split(before, "+")
        before = result[0]
        before = strings.Replace(before, ".", "", -1)
        m[before + "@" + after] = 1
    }
    
    return len(m)
}

func Split(s, sep string) []string

// n 表示替换前几个匹配到的字符串，n 为 -1 时，没有数量限制
func Replace(s, old, new string, n int) string

func Index(s, substr string) int