Fill in the given format and any unknowns with a * and the program will replace the *s with possible variations. Read through the output to try and figure out the string that you forgot.

PermutationGenerator.kt

fun main() {
    // Type what you know here, and replace unknowns with the star symbol (*). The more star symbols you have
    // the more permutations you will have. This increases exponentially.
    val givenFormat = "myemailwithm**singcha*s@gmail.com"

    // DO NOT CHANGE ANYTHING BEYOND THIS LINE
    val generator = PermutationGenerator(givenFormat)
    generator.generate()
}

class PermutationGenerator(
    private val givenFormat: String
) {
    private val unknownIndices = HashSet<Int>()

    init {
        givenFormat.toCharArray().forEachIndexed { idx, c ->
            if (c == '*') {
                unknownIndices.add(idx)
            }
        }
    }

    fun generate() {
        println("Generating permutations...")
        generate(unknownIndices.size, "")
    }

    private fun generate(length: Int, current: String) {
        if (current.length < length) {
            var c = 'A'
            while (c <= 'z') {
                generate(length, current + c)
                c++
            }
        } else {
            var idx = 0
            var newStr = givenFormat
            unknownIndices.forEach {
                val chars = newStr.toCharArray()
                chars[it] = current[idx]
                newStr = String(chars)
                idx++
            }

            println("Email permutation: $newStr")
        }
    }
}