package main
import (
"fmt"
"strconv"
)
/*
Program: Print numbers with a thousand separator as spaces in Go.
Architecture notes:
-------------------
- Go's fmt package does not support custom thousand separators.
- We implement a manual formatter:
* Convert the number to a string.
* Handle negative numbers cleanly.
* Insert spaces every three digits from the left.
- The function is modular, reusable, and efficient.
Performance notes:
------------------
- O(n) time where n is the number of digits.
- Memory usage is minimal; only small strings are created.
- No external libraries; uses only standard Go features.
Pitfalls:
---------
- Must preserve the minus sign for negative numbers.
- Must ensure correct grouping even for very large integers.
- Avoid formatting floats unless converted to integers first.
Security notes:
---------------
- No external input parsing; safe for demonstration.
- Avoid printing sensitive values in real systems.
Tests:
------
- Positive numbers
- Negative numbers
- Zero
- Very large integers
*/
// FormatWithSpaces formats an integer using spaces as thousand separators.
func FormatWithSpaces(n int64) string {
// Convert number to string
s := strconv.FormatInt(n, 10)
// Handle negative numbers
isNegative := s[0] == '-'
digits := s
if isNegative {
digits = s[1:]
}
// Determine how many digits before the first space
lenDigits := len(digits)
firstGroup := lenDigits % 3
if firstGroup == 0 {
firstGroup = 3
}
// Build result
result := ""
if isNegative {
result = "-"
}
// First group
result += digits[:firstGroup]
// Remaining groups
pos := firstGroup
for pos < lenDigits {
result += " " + digits[pos:pos+3]
pos += 3
}
return result
}
func main() {
tests := []int64{
0,
42,
1234,
987654321,
-1234567,
1000000000000000000, // 10^18
}
fmt.Println("Running test cases:\n")
for _, n := range tests {
fmt.Println("Original: ", n)
fmt.Println("Formatted:", FormatWithSpaces(n), "\n")
}
}
/*
run:
Running test cases:
Original: 0
Formatted: 0
Original: 42
Formatted: 42
Original: 1234
Formatted: 1 234
Original: 987654321
Formatted: 987 654 321
Original: -1234567
Formatted: -1 234 567
Original: 1000000000000000000
Formatted: 1 000 000 000 000 000 000
*/
