find the difference between two strings

To find the difference between two strings where one string is a permutation of another string with one additional character, you can use bit manipulation in Kotlin. This approach leverages the XOR operator to cancel out pairs of identical characters, leaving only the additional character as the result.

Here’s how you can implement a function in Kotlin to find the difference:

fun findTheDifference(s: String, t: String): Char {
    var charCode = 0
    for (char in s) {
        charCode = charCode xor char.toInt()
    }
    for (char in t) {
        charCode = charCode xor char.toInt()
    }
    return charCode.toChar()
}

fun main() {
    val s = "abcd"
    val t = "abcde"
    println("The added character is: ${findTheDifference(s, t)}")
}

Explanation:

• Loop through s: First, we loop through each character in the first string s, converting each character to its integer ASCII value using toInt() and then applying the XOR operation with charCode. Initially, charCode is set to 0. XORing any number with 0 leaves it unchanged, so after this loop, charCode effectively contains the XOR of all characters in s.
• Loop through t: Next, we perform the same operation for the second string t. Since t contains all the characters in s plus one additional character, after this loop, all characters that appear in both s and t will cancel out because XORing a number with itself results in 0. Therefore, charCode will now hold the ASCII value of the additional character.
• Convert to Char and Return: Finally, we convert charCode back to a character using toChar() and return it as the result.

This approach efficiently finds the added character with a time complexity of O(n) and without using any additional data structures, by exploiting the property of the XOR operation that a xor a = 0 and a xor 0 = a.