Kotlin Pattern Printing: Stars + Number Triangle (Beginner Friendly)

import kotlin.math.max

fun main() {
    println("Kotlin Pattern Printing (Stars + Numbers)")
    print("Enter a size (1..50): ")

    val input = readLine()?.trim()
    val n = input?.toIntOrNull()

    if (n == null) {
        println("Error: Please enter a valid whole number (e.g., 5).")
        return
    }
    if (n !in 1..50) {
        println("Error: Size must be between 1 and 50.")
        return
    }

    printSolidSquare(n)
    printHollowSquare(n)
    printRightTriangleStars(n)
    printPyramidStars(n)
    printNumberTriangle(n)

    /*
    SAMPLE OUTPUT (n = 5)

    Solid Square (Stars)
    *****
    *****
    *****
    *****
    *****

    Hollow Square (Stars)
    *****
    *   *
    *   *
    *   *
    *****

    Right Triangle (Stars)
    *
    **
    ***
    ****
    *****

    Pyramid (Stars)
        *
       ***
      *****
     *******
    *********

    Number Triangle
    1
    1 2
    1 2 3
    1 2 3 4
    1 2 3 4 5
    */
}

fun repeatChar(ch: Char, times: Int): String {
    val safeTimes = max(0, times)
    return buildString {
        repeat(safeTimes) { append(ch) }
    }
}

fun repeatText(text: String, times: Int): String {
    val safeTimes = max(0, times)
    return buildString {
        repeat(safeTimes) { append(text) }
    }
}

fun printSolidSquare(n: Int) {
    println()
    println("Solid Square (Stars)")
    val line = repeatChar('*', n)
    repeat(n) { println(line) }
}

fun printHollowSquare(n: Int) {
    println()
    println("Hollow Square (Stars)")

    if (n == 1) {
        println("*")
        return
    }

    val topBottom = repeatChar('*', n)
    val middle = "*" + repeatChar(' ', n - 2) + "*"

    println(topBottom)
    repeat(n - 2) { println(middle) }
    println(topBottom)
}

fun printRightTriangleStars(n: Int) {
    println()
    println("Right Triangle (Stars)")
    for (i in 1..n) {
        println(repeatChar('*', i))
    }
}

fun printPyramidStars(n: Int) {
    println()
    println("Pyramid (Stars)")
    for (i in 1..n) {
        val spaces = n - i
        val stars = 2 * i - 1
        println(repeatChar(' ', spaces) + repeatChar('*', stars))
    }
}

fun printNumberTriangle(n: Int) {
    println()
    println("Number Triangle")
    for (i in 1..n) {
        val row = buildString {
            for (j in 1..i) {
                if (j > 1) append(' ')
                append(j)
            }
        }
        println(row)
    }
}