import Foundation
/// Swaps two ASCII characters in a string in-place using the XOR swap algorithm.
///
/// - Note: This function demonstrates bitwise XOR swapping for educational purposes.
/// In production Swift code, preferred idioms such as `text.swapAt(index1, index2)`
/// or tuple assignment `(a, b) = (b, a)` are strongly recommended for safety,
/// clarity, and performance.
///
/// - Parameters:
/// - text: The string containing the characters to swap (passed in-place via `inout`).
/// - left: Zero-based integer index of the first character.
/// - right: Zero-based integer index of the second character.
func xorSwapCharacters(_ text: inout String, left: Int, right: Int) {
var bytes = Array(text.utf8)
// Guard clause for empty string or out-of-bounds indices
guard !bytes.isEmpty, left >= 0, right >= 0, left < bytes.count, right < bytes.count else {
return
}
// XOR swap fails if left == right because (x ^ x) evaluates to 0
guard left != right else {
return
}
// Bitwise XOR swap on UInt8 elements
bytes[left] ^= bytes[right]
bytes[right] ^= bytes[left]
bytes[left] ^= bytes[right]
// Construct valid UTF-8 string back from modified bytes
if let updatedText = String(bytes: bytes, encoding: .utf8) {
text = updatedText
}
}
func main() {
var text = "hello"
print("Before: \(text)")
xorSwapCharacters(&text, left: 1, right: 4)
print("After: \(text)")
}
main()
/*
run:
Before: hello
After: holle
*/
