Reverse a Number (JavaScript)

Reversing a number means taking its digits and arranging them in reverse order. For example, reversing 123 gives 321. This is a common logical programming problem that helps to practice arithmetic operations and loop control.

The core idea involves extracting the last digit of the number, appending it to a reversed number, and then removing that last digit from the original number until the original number becomes zero. This process typically uses the modulo operator (%) to get the last digit and integer division (Math.floor()) to remove it.

This is the most common and explicit way to reverse a number digit by digit.

Explanation:

• reversedNum is initialized to 0.
• The while loop continues as long as originalNum is greater than 0.
• lastDigit = originalNum % 10; extracts the rightmost digit.
• reversedNum = reversedNum * 10 + lastDigit; builds the reversed number. Multiplying by 10 shifts existing digits to the left.
• originalNum = Math.floor(originalNum / 10); removes the rightmost digit from originalNum.
• Special handling for negative numbers: reverse the absolute value and then apply the negative sign back.

This method leverages string manipulation functions available in JavaScript, often leading to more concise code, especially for positive integers.

Explanation:

• The number is converted to its absolute value string representation.
• split('') converts the string into an array of characters.
• reverse() reverses the order of elements in the array.
• join('') concatenates the array elements back into a string.
• Finally, Number() converts the reversed string back to a number.
• The original sign is reapplied.

• Modulo and Division: Essential for digit-by-digit processing of numbers.
• Type Conversion: Converting between numbers and strings can simplify certain problems.
• Handling Edge Cases: Consider negative numbers and numbers ending in zero (e.g., reversing 120 should yield 21, not 021, which Number() handles correctly).
• Efficiency: The iterative method (Method 1) is generally more efficient for very large numbers as it avoids string conversions, though for typical integer sizes, the string method is often clear enough.