Middle Character swift - swift

Question

I have an issue I am trying to solve
I am trying to find middle character of the word. If the word's length is odd, return the middle character. If the word's length is even, return the middle 2 characters
func middle(_ str: String) -> String {
let arr = Array(str).map{$0}
print(arr)
// if arr.count
for myInt: String in arr {
if myInt % 2 == 0 {
println("\(myInt) is even number")
} else {
println("\(myInt) is odd number")
}
}
return ""
}

Answer 1

Assuming that your string is the whole word (otherwise you would need to enumerate your string byWords before using this property):
extension StringProtocol {
var middle: SubSequence {
if isEmpty { return "" }
if count == 1 { return self[startIndex...startIndex] }
let middleIndex = index(startIndex, offsetBy: count/2)
let previous = index(before: middleIndex)
return count % 2 == 0 ? self[previous...middleIndex] : self[middleIndex...middleIndex]
}
}
"abc".middle
"abcd".middle

Answer 2

You could use this function:
func middle(_ str: String) -> String {
let count = str.count
if count < 2 {
return str
}
let start = str.index(str.startIndex, offsetBy: (count - 1)/2)
let end = str.index(str.startIndex, offsetBy: (count + 2)/2)
return String(str[start..<end])
}
Here are some use cases:
middle("") //""
middle("1") //"1"
middle("12") //"12"
middle("123") //"2"
middle("1234") //"23"
middle("12345") //"3"

Answer 3

Let's try to approach this systematically. The first task would be to determine the offsets of the first and last character of the “middle part”. If we make a table with some representative cases
string result length first last
------------------------------------
a a 1 0 0
ab ab 2 0 1
abc b 3 1 1
abcd bc 4 1 2
abcde c 5 2 2
abcdef cd 6 2 3
then we can derive that
firstIndex = (length - 1) / 2
lastIndex = length / 2
where / is the truncating integer division. An empty string has to be treated separately.
Finally we need to know how to work with indices and offsets in a Swift string, which is explained in A New Model for Collections and Indices.
This leads to the implementation
func middle(_ str: String) -> String {
if str.isEmpty { return "" }
let len = str.count
let fromIdx = str.index(str.startIndex, offsetBy: (len - 1)/2)
let toIdx = str.index(str.startIndex, offsetBy: len/2)
return String(str[fromIdx...toIdx])
}

Answer 4

here is one more example:
add this extension
extension StringProtocol {
subscript(offset: Int) -> Element {
return self[index(startIndex, offsetBy: offset)]
}
subscript(range: CountableClosedRange<Int>) -> SubSequence {
return prefix(range.lowerBound + range.count)
.suffix(range.count)
}
}
use this like
let stringLength: Int = str.count
if stringLength % 2 == 0{
//even
print(str[((stringLength/2) - 1)...(stringLength/2)])
}else{
//odd
print(str[(stringLength/2) - 1])
}