How do you reverse a string?

To reverse a string means to create a new string that is the exact opposite of the original string, with characters appearing in the reverse order. This is a common operation in programming and can be done in several ways depending on the programming language used. Here’s a detailed explanation and code examples for reversing a string in different languages:

Conceptual Explanation

1. Understanding the Problem:

• Input: A string, for example, “hello”.
• Output: A new string where the characters are in reverse order, for example, “olleh”.

1. Approaches:

• Using Built-in Functions: Many programming languages have built-in functions or methods to reverse strings.
• Manual Reversal: By iterating through the string and constructing the reversed string manually.

Code Examples

Python

Using Slicing:

def reverse_string(s):
    return s[::-1]

# Example usage
original = "hello"
reversed_string = reverse_string(original)
print(reversed_string)  # Output: "olleh"

Manual Method:

def reverse_string(s):
    reversed_str = ''
    for char in s:
        reversed_str = char + reversed_str
    return reversed_str

# Example usage
original = "hello"
reversed_string = reverse_string(original)
print(reversed_string)  # Output: "olleh"

JavaScript

Using Built-in Methods:

function reverseString(s) {
    return s.split('').reverse().join('');
}

// Example usage
const original = "hello";
const reversedString = reverseString(original);
console.log(reversedString);  // Output: "olleh"

Manual Method:

function reverseString(s) {
    let reversedStr = '';
    for (let i = s.length - 1; i >= 0; i--) {
        reversedStr += s[i];
    }
    return reversedStr;
}

// Example usage
const original = "hello";
const reversedString = reverseString(original);
console.log(reversedString);  // Output: "olleh"

Java

Using StringBuilder:

public class Main {
    public static String reverseString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static void main(String[] args) {
        String original = "hello";
        String reversedString = reverseString(original);
        System.out.println(reversedString);  // Output: "olleh"
    }
}

Manual Method:

public class Main {
    public static String reverseString(String s) {
        char[] charArray = s.toCharArray();
        int left = 0;
        int right = charArray.length - 1;

        while (left < right) {
            char temp = charArray[left];
            charArray[left] = charArray[right];
            charArray[right] = temp;
            left++;
            right--;
        }

        return new String(charArray);
    }

    public static void main(String[] args) {
        String original = "hello";
        String reversedString = reverseString(original);
        System.out.println(reversedString);  // Output: "olleh"
    }
}

Summary

• Python: Use slicing [::-1] or build the string manually.
• JavaScript: Use split, reverse, and join methods or manually construct the reversed string.
• Java: Use StringBuilder or manually swap characters in an array.

Each method has its own advantages, with built-in functions generally being more concise and manual methods offering more control over the process.