What is the swift way of converting this string into PGN notation? - swift

Question

I have the following string
let a:String = "r0bqkb0r/pppppppp/00n00n00/00000000/000P0000/0000B000/PPP0PPPP/RN0QKBNR/"
and want to convert this to PGN notation so the final result should be
result = "r1bqkb1r/pppppppp/2n2n2/8/3P4/4B3/PPP1PPPP/RN1QKBNR/"
The PGN notation converts the zeros to counts found. Normally in python, I would just use
import chess.pgn
Before deep diving into python library, is there is a succinct and 'Swift' way to do this?

Answer 1

Here is a solution using reduce and a separate counter
Update, rewrote it as an extension to String
extension String {
func pgpNotation() -> String {
var zeroCounter = 0
var result = self.reduce(into: "") {
if $1 == "0" {
zeroCounter += 1
return
}
if zeroCounter > 0 {
$0.append("\(zeroCounter)")
zeroCounter = 0
}
$0.append($1)
}
if zeroCounter > 0 { result.append("\(zeroCounter)")}
return result
}
}
Examples
let x = "r00d00"
print(x.pgpNotation())
let a:String = "r0bqkb0r/pppppppp/00n00n00/00000000/000P0000/0000B000/PPP0PPPP/RN0QKBNR/"
print(a.pgpNotation())
r2d2
r1bqkb1r/pppppppp/2n2n2/8/3P4/4B3/PPP1PPPP/RN1QKBNR/

Answer 2

There is no direct function for that but I just created a program for fun. You can check this out:-
let str = "r0bqkb0r/pppppppp/00n00n00/00000000/000P0000/0000B000/PPP0PPPP/RN0QKBNR/"
var newStr = ""
var flag = 0
// Do any additional setup after loading the view.
for char in str {
if flag == 0 {
if char == "0" {
flag += 1
}
else {
newStr.append(char)
}
}
else {
if char == "0" {
flag += 1
}
else {
newStr.append("\(flag)")
flag = 0
if char == "0" {
flag += 1
}
else {
newStr.append(char)
}
}
}
}
print(newStr)

Answer 3

There doesn't exist any direct method to get the pgn notation String. You can use a forEach(_:) instead, i.e.
let a = "r0bqkb0r/pppppppp/00n00n00/00000000/000P0000/0000B000/PPP0PPPP/RN0QKBNR/"
var result = ""
var count = 0
a.forEach {
if $0 == "0" {
count += 1
} else {
if count != 0 {
result.append("\(count)")
count = 0
}
result.append($0)
}
}
print(result) //r1bqkb1r/pppppppp/2n2n2/8/3P4/4B3/PPP1PPPP/RN1QKBNR/

Answer 4

With a simple regex and a loop (just to propose an original solution):
let a = "r0bqkb0r/pppppppp/00n00n00/00000000/000P0000/0000B000/PPP0PPPP/RN0QKBNR/"
extension String {
var chessPGN : String {
var result = self
let regex = try! NSRegularExpression(pattern: "0+")
while let match = regex.matches(in: result, range: .init(location: 0, length: result.count)).first {
if let stringRange = Range(match.range , in: result) {
result.replaceSubrange(stringRange, with: match.range.length.description)
}
}
return result
}
}
print(a.chessPGN) // r1bqkb1r/pppppppp/2n2n2/8/3P4/4B3/PPP1PPPP/RN1QKBNR/
EDIT: A version calling only once the regex
extension String {
var chessPGN : String {
var result = self
let regex = try! NSRegularExpression(pattern: "0+")
for match in regex.matches(in: result, range: .init(location: 0, length: result.count)).sorted(by: { $0.range.location > $1.range.location }) {
if let stringRange = Range(match.range , in: result) {
result.replaceSubrange(stringRange, with: match.range.length.description)
}
}
return result
}
}