Reverse an Integer

📌 Definition:

📖 Detailed Explanation:

Repeatedly take the last digit with % 10 and build the reversed number as result = result * 10 + digit, dividing the input by 10 each step. Handle the sign separately or let it fall out of integer math. Watch for overflow when the reversed value exceeds the integer range.

💻 Solutions:

• Java
• JavaScript
• Python

public static int reverseInt(int n) {
    long r = 0;
    while (n != 0) { r = r * 10 + n % 10; n /= 10; }
    if (r > Integer.MAX_VALUE || r < Integer.MIN_VALUE) return 0; // overflow
    return (int) r;
}

function reverseInt(n) {
  const sign = Math.sign(n);
  const r = parseInt(String(Math.abs(n)).split('').reverse().join(''), 10);
  return r > 2147483647 ? 0 : sign * r;
}

def reverse_int(n):
    sign = -1 if n < 0 else 1
    r = sign * int(str(abs(n))[::-1])
    return r if -2**31 <= r <= 2**31 - 1 else 0

🔑 Key Points:

• Extract digits with %10 and /10
• result = result*10 + digit
• Preserve the sign
• Guard against overflow of the reversed value

🌍 Real-World Example: