为什么此快捷功能不起作用？

Question

This function takes two string arguments. It is supposed to return the first one as dashes except where the character is somewhere inside of the second argument. Example:

dashes_except("hello", except: "lo") -> --llo

The function works fine when the except argument is only one letter but fails when it is longer than one. It just returns dashes. I'm pretty new to Swift so some help would be super appreciated!

Here is the code:

func dashes_except(word: String,except: String) -> String { 

    var loc = [String]()
    for (index, character) in enumerate(word) {
        loc.append(String(character))
    }
    var loc_except = [String]()
    for (index, character) in enumerate(except) {     
        loc_except.append(String(character))
    }
    for x in 0..<loc.count {
        for y in 0..<loc_except.count {
            if loc[x] != loc_except[y] {
                loc[x] = "-"
            }  
        }   
    }
    return "".join(loc)
}

Answer 1

In the inner loop

    for y in 0..<loc_except.count {
        if loc[x] != loc_except[y] {
            loc[x] = "-"
        }
    }

loc[x] is replaced by the dash "-" if it is different from any characters in loc_except . This will always be the case if the exception string has at least two different characters.

You can solve this using contains() :

for x in 0..<loc.count {
    if !contains(loc_except, loc[x]) {
        loc[x] = "-"
    }
}

That being said, your function can be concisely written as

func dashes_except(word: String,except: String) -> String {

    return String(Array(word).map( { contains(except, $0) ? $0 : "-" } ))
}

Here,

• Array(word) creates an array with all the characters in the string (what you did with the enumerate() loop),
• map { } replaces all characters which are not contained in the exception string by a dash, and
• String( ... ) converts the character array to a string again (what you did with "".join() ).