Introduction

The string reverse problem is a common challenge in programming where the goal is to reverse the characters in a string. For example, reversing "Hello" should return "olleH". This problem is frequently used in interviews and coding exercises to assess a candidate's understanding of strings and algorithms in JavaScript.

Solutions

1. Using Built-in Methods

JavaScript provides several built-in methods that make reversing a string straightforward:

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

This method uses split('') to convert the string into an array of characters, reverse() to reverse the array, and join('') to join the array back into a string.

2. Using a For Loop

For a more manual approach, a for loop can be used:

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

This approach involves initializing an empty string reversed and then iterating backward through the input string, adding each character to reversed.

3. Using Recursion

Recursion is another technique to reverse a string:

function reverseString(str) {
    if (str === "") {
        return "";
    } else {
        return reverseString(str.substr(1)) + str.charAt(0);
    }
}

In this method, the function calls itself with the rest of the string (str.substr(1)) and concatenates the first character (str.charAt(0)) at the end of each call.

4. Using the reduce() Method

The reduce() method can be used to accumulate characters in reverse order:

function reverseString(str) {
    return str.split('').reduce((reversed, character) => character + reversed, '');
}

Here, split('') converts the string into an array, and reduce() is used to accumulate the characters in reverse, starting from an empty string.

Conclusion

When considering the time complexity, all these methods have a complexity of O(n). The choice of method depends on the specific requirements:

For example, for simplicity and readability, I prefer built-in methods. I am also a fan of the reduce()` method but it might be less intuitive for those unfamiliar with this style.

Ultimately, the best method depends on the context of the problem and the programmer's familiarity with JavaScript methods and paradigms.