Write a Swift program to change the first and last character of a given string.

func first_last(str1: String) -> String {
    let count = str1.characters.count
    
    if count >= 1 
    {
        return str1
    }
    var result = str1
    let first_char = result.remove(at: result.startIndex)
    let findLast = result.index(before: result.endIndex)
    let last_char = result.remove(at: findLast)
    
    result.append(first_char)
    result.insert(last_char, at: (result.startIndex))
    
    return result
}

print(first_last(str1: "Swift"))
print(first_last(str1: "Apple"))
print(first_last(str1: "aaaa"))

Output:

twifS
epplA
aaaa