Bradley Scott Maskell Bradley Scott Maskell - 2 years ago 127
Swift Question

Finding the first non-repeating character in a String using Swift

This finds the duplicates in the array, but i'm looking for something that finds the first non-repeating character in a string. I've been trying to figure out a way to do this and I cannot figure it out. This is the closest i've gotten.

var strArray = ["P","Q","R","S","T","P","R","A","T","B","C","P","P","P","P","P","C","P","P","J"]


var filter = Dictionary<String,Int>()
var len = strArray.count
for var index = 0; index < len ;++index {
var value = strArray[index]
if (filter[value] != nil) {
filter[value] = 1

Answer Source

In order to tell if a character repeats itself, go through the entire array once, incrementing the count of occurrences in a dictionary:

let characters = ["P","Q","R","S","T","P","R","A","T","B","C","P","P","P","P","P","C","P","P","J"]

var counts: [String: Int] = [:]
for character in characters {
    counts[character] = (counts[character] ?? 0) + 1

let nonRepeatingCharacters = characters.filter({counts[$0] == 1})
// ["Q", "S", "A", "B", "J"]
let firstNonRepeatingCharacter = nonRepeatingCharacters.first!
// "Q"
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