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Reversing Words in a String

Reversing the order of words in a string is a common problem that can be encountered in coding interviews.

Problem Statement

Given a string, reverse the order of words. Each word is separated by spaces, and you need to ensure that the reversed words are also separated by a single space.

Example

Input: "Hello World from Rowdy Coders"
Output: "Coders Rowdy from World Hello"

Approach 1: Using Built-in Methods

The simplest way to reverse the words in a string is by leveraging JavaScript’s built-in methods. Here are the steps:

  1. Split the string into an array of words.
  2. Reverse the array.
  3. Join the array back into a string.
function reverseWords(str) {
  return str.split(' ').reverse().join(' ');
}

// Test the function
const input = "Hello World from Rowdy Coders";
const output = reverseWords(input);
console.log(output); // Output: "Coders Rowdy from World Hello"

Explanation

  1. split(' ') converts the string into an array of words.
  2. reverse() reverses the array.
  3. join(' ') combines the reversed array into a single string with spaces between words.

Approach 2: Using a Loop

If you want to avoid using built-in methods like reverse(), you can reverse the words using a loop. This approach gives you more control over the process.

function reverseWords(str) {
  const words = str.split(' ');
  let reversedWords = '';
  
  for (let i = words.length - 1; i >= 0; i--) {
    reversedWords += words[i] + (i > 0 ? ' ' : '');
  }
  
  return reversedWords;
}

// Test the function
const input = "Hello World from Rowdy Coders";
const output = reverseWords(input);
console.log(output); // Output: "Coders Rowdy from World Hello"

Explanation

  1. split(' ') converts the string into an array of words.
  2. A loop iterates over the array in reverse order, building the reversed string one word at a time.
  3. The loop ensures that a space is added between words except after the last word.

Approach 3: Using a Stack

A stack is a suitable data structure for reversing the order of elements. You can push words onto the stack and then pop them off to reverse their order.

function reverseWords(str) {
  const words = str.split(' ');
  const stack = [];
  
  for (const word of words) {
    stack.push(word);
  }
  
  let reversedWords = '';
  while (stack.length > 0) {
    reversedWords += stack.pop() + (stack.length > 0 ? ' ' : '');
  }
  
  return reversedWords;
}

// Test the function
const input = "Hello World from Rowdy Coders";
const output = reverseWords(input);
console.log(output); // Output: "Coders Rowdy from World Hello"

Explanation

  1. split(' ') converts the string into an array of words.
  2. Each word is pushed onto the stack.
  3. Words are popped off the stack and concatenated into the reversed string.

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