/*
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 Swift'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.
func countDigits(_ value: Int) -> Int {
if value == 0 { return 1 } // zero has one digit
var n = abs(value)
var count = 0
while n > 0 {
n /= 10
count += 1
}
return count
}
// Returns true if the number has an even number of digits.
func hasEvenDigits(_ value: Int) -> Bool {
countDigits(value) % 2 == 0
}
// Count how many numbers in an array have an even number of digits.
// Complexity: O(n)
func countEvenDigitNumbers(_ arr: [Int]) -> Int {
arr.filter { hasEvenDigits($0) }.count
}
// Utility: print an array in a readable format.
func printArray(_ arr: [Int]) {
print("[ ", terminator: "")
arr.forEach { print("\($0) ", terminator: "") }
print("]")
}
// ------------------------------------------------------------
// Main: multiple test cases, including edge cases.
// ------------------------------------------------------------
print("=== Count Numbers with Even Number of Digits (Swift) ===\n")
// Test cases
let a1 = [12, 345, 2, 6, 7896]
let a2 = [0, -22, 1000, -7]
let a3 = [1, 3, 5] // No even-digit numbers
let a4 = [10, 99, 1001] // All even-digit numbers
let a5: [Int] = [] // Edge case: empty array
let a6 = [-100000, 500000] // Large numbers
// Test 1
print("Test 1: ", terminator: "")
printArray(a1)
print(" -> Count = \(countEvenDigitNumbers(a1))")
// Test 2
print("Test 2: ", terminator: "")
printArray(a2)
print(" -> Count = \(countEvenDigitNumbers(a2))")
// Test 3
print("Test 3: ", terminator: "")
printArray(a3)
print(" -> Count = \(countEvenDigitNumbers(a3))")
// Test 4
print("Test 4: ", terminator: "")
printArray(a4)
print(" -> Count = \(countEvenDigitNumbers(a4))")
// Test 5: empty array
print("Test 5: ", terminator: "")
printArray(a5)
print(" -> Count = \(countEvenDigitNumbers(a5))")
// Test 6: large numbers
print("Test 6: ", terminator: "")
printArray(a6)
print(" -> Count = \(countEvenDigitNumbers(a6))")
/*
run:
=== Count Numbers with Even Number of Digits (Swift) ===
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
*/
