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.