/*
Architecture notes:
-------------------
This program demonstrates a modular design:
- countDigits: counts digits using integer math.
- hasEvenDigits: checks if a number has an even digit count.
- countEvenDigitNumbers: processes an array and returns the count.
- Multiple test cases in main.
Performance notes:
------------------
- All operations are O(n) for n array elements.
- Digit counting uses integer division, avoiding string conversions.
- Negative numbers handled safely.
- Uses Kotlin's standard library for clarity and safety.
Security notes:
---------------
- No unsafe operations.
- No unchecked indexing.
- No external dependencies.
*/
// Count the number of digits in an integer.
// Complexity: O(log n) due to repeated division by 10.
// Pitfall: negative numbers must be handled correctly.
fun countDigits(value: Int): Int {
if (value == 0) return 1 // zero has one digit
var n = kotlin.math.abs(value)
var count = 0
while (n > 0) {
n /= 10
count++
}
return count
}
// Returns true if the number has an even number of digits.
fun hasEvenDigits(value: Int): Boolean =
countDigits(value) % 2 == 0
// Count how many numbers in an array have an even number of digits.
// Complexity: O(n)
fun countEvenDigitNumbers(arr: IntArray): Int =
arr.count { hasEvenDigits(it) }
// Utility: print an array in a readable format.
fun printArray(arr: IntArray) {
print("[ ")
arr.forEach { print("$it ") }
print("]")
}
fun main() {
println("=== Count Numbers with Even Number of Digits (Kotlin) ===")
println()
// Test cases
val a1 = intArrayOf(12, 345, 2, 6, 7896)
val a2 = intArrayOf(0, -22, 1000, -7)
val a3 = intArrayOf(1, 3, 5) // No even-digit numbers
val a4 = intArrayOf(10, 99, 1001) // All even-digit numbers
val a5 = intArrayOf() // Edge case: empty array
val a6 = intArrayOf(-100000, 500000) // Large numbers
// Test 1
print("Test 1: ")
printArray(a1)
println(" -> Count = ${countEvenDigitNumbers(a1)}")
// Test 2
print("Test 2: ")
printArray(a2)
println(" -> Count = ${countEvenDigitNumbers(a2)}")
// Test 3
print("Test 3: ")
printArray(a3)
println(" -> Count = ${countEvenDigitNumbers(a3)}")
// Test 4
print("Test 4: ")
printArray(a4)
println(" -> Count = ${countEvenDigitNumbers(a4)}")
// Test 5: empty array
print("Test 5: ")
printArray(a5)
println(" -> Count = ${countEvenDigitNumbers(a5)}")
// Test 6: large numbers
print("Test 6: ")
printArray(a6)
println(" -> Count = ${countEvenDigitNumbers(a6)}")
}
/*
run:
=== Count Numbers with Even Number of Digits (Kotlin) ===
Test 1: [ 12 345 2 6 7896 ] -> Count = 2
Test 2: [ 0 -22 1000 -7 ] -> Count = 2
Test 3: [ 1 3 5 ] -> Count = 0
Test 4: [ 10 99 1001 ] -> Count = 3
Test 5: [ ] -> Count = 0
Test 6: [ -100000 500000 ] -> Count = 2
*/
