Code to compress a string in Swift. Example : AAABBACC to A3B2AC2

gistfile1.txt

// String to compress
let stringtoCompress = "AAABBACC"

// Empty string to store compressed value
var compressedString = ""

// Store the letter count to append in compressed string
var letterCountStored:Int

//Initially letterCountStored is set to 0
letterCountStored = 0

// function the compress given string
func compressString(string2Compress: String) ->(String) {
    
    // get string length
    let letterCount = string2Compress.count
  
    // convert to int
    let letterCountInt = Int(letterCount)
  
    // check if string has more than 1 letter
    if letterCountInt == 1 {
        compressedString = string2Compress
    } else {
        //reduce 1 from characters count
        let stringlenth = letterCountInt-1
        
        //check all letters in string
        for i in 0 ..< stringlenth {
            // fetching first letter to compare
            let index = string2Compress.index(string2Compress.startIndex,offsetBy:i)
            let firstLetterToCompare = string2Compress[index]
            
            // fetching second letter to compare
            let secondIndex = string2Compress.index(string2Compress.startIndex,offsetBy:i+1)
            let secondLetterToCompare = string2Compress[secondIndex]
            
            //pass the above 2 letters to function to compare
            compareTwoConsecutiveLetters(firstLetter: firstLetterToCompare, secondLetter: secondLetterToCompare)
            
            //Check if comparing the last two letters
            if i == stringlenth - 1 {
                // append last letter count to compressed string
                appendLetterCount()
            }
        }
    }
    // return compressed string
    return compressedString
}

// function to compare two consecutive letters
func compareTwoConsecutiveLetters(firstLetter : Character, secondLetter : Character){
    
    // chcek if letters are same
    if firstLetter == secondLetter {
        
        // add one to the letter count ie 0 to 1
        letterCountStored += 1
        
        //check if string is empty
        if compressedString.isEmpty == true {
            
            //add first letter to compressed string
            compressedString = compressedString + String(firstLetter)
            
            // since first 2 letters are same add one to the letter count ie 1 to 2
            letterCountStored += 1
        }
    }
    else {
        
        // check if compressed string is empty
        if compressedString.isEmpty == true {
            
            // add one to the letter count
            letterCountStored += 1
            
            // append first letter to compressed string
            compressedString = compressedString + String(firstLetter)
            
            // append first letter count to compressed string
            appendLetterCount()
            
            // append second letter to compressed string
            compressedString = compressedString + String(secondLetter)
            
            // reset the letter count
            letterCountStored = 1
            
            
        }
            // if compressed string alredy has first letter
        else if compressedString.count==1 {
            
            // add one to the letter count
            // letterCountStored += 1
            
            /// append first letter count to compressed string
            appendLetterCount()
            
            // append second letter to compressed string
            compressedString = compressedString + String(secondLetter)
            
            // reset the letter count
            letterCountStored = 1
        }
        else {
            // append first letter count to compressed string
            appendLetterCount()
            
            // append second letter to compressed string
            compressedString = compressedString + String(secondLetter)
            
            // reset the letter count
            letterCountStored = 1
        }
    }
}



// function to append letter count
func appendLetterCount(){
    
    // check if letter occurs more than once
    if letterCountStored > 1 {
        
        //append to compressed string
        compressedString = compressedString + String(letterCountStored)
        
    }
}


//pass the string to compress to compressString function
var compressedStringOutput = compressString(string2Compress: stringtoCompress)
print(compressedStringOutput)