Reverse all the Words of Sentence JavaScript

Given a sentence, Our task is to reverse all the words in the sentence while maintaining their order.

Example: 

Input:  "Hello World"
Output: "olleH dlroW"

Below are the approaches to reverse all the words of sentence JavaScript:

Using Built-in Functions

In this approach, The function reverseWords takes a sentence as input, splits it into an array of words, iterates through each word to reverse it, and then joins the reversed words back into a sentence. Finally, it returns the reversed sentence.

Example: The example below shows the program to reverse all the words of a sentence using Built-in Functions.

function reverseWords(sentence) {
  let words = sentence.split(" ");
  for (let i = 0; i < words.length; i++) {
    words[i] = words[i].split("").reverse().join("");
  }
  let reversed = words.join(" ");
  return reversed;
}

let input = "Hello World";
let output = reverseWords(input);
console.log(output);

olleH dlroW

Time Complexity: O(n * m), where n is the number of words in the sentence and m is the average length of each word.

Auxiliary Space: O(n).

Using Iterative Reversal

In this approach, we iterate through each character of the input sentence and if we encounter a space, we add the current word (substring from the last space encountered to the current position) reversed to the result string. Then, we reverse the last word append it to the result, and print the reversed sentence.

Example: Implementation of a program to reverse all the words of a sentence using Iterative Reversal

function reverse(sentence) {
    let reversed = ""; 
    let start = 0;

    for (let i = 0; i < sentence.length; i++) {
        if (sentence[i] === " ") {
            reversed += revStr(sentence.substring(start, i)) + " ";
            start = i + 1;
        }
    }

    reversed += revStr(sentence.substring(start));
    return reversed;
}

function revStr(str) {
    let rev = "";
    for (let i = str.length - 1; i >= 0; i--) {
        rev += str[i];
    }
    return rev;
}

let input = "Hello World";
let output = reverse(input);
console.log(output);

olleH dlroW

Time Complexity: O(n), where n is the length of the input sentence.

Auxiliary Space: O(n).

Using Stack for Reversal

In this approach, we iterate through each character of the input sentence and use a stack to reverse the characters of each word. When we encounter a space, we pop all characters from the stack to get the reversed word and add it to the result string. Finally, we handle the last word separately after the loop.

Example: Implementation of a program to reverse all the words of a sentence using a stack.

function reverseWithStack(sentence) {
    let stack = [];
    let reversed = "";
    
    for (let i = 0; i < sentence.length; i++) {
        if (sentence[i] !== " ") {
            stack.push(sentence[i]);
        } else {
            while (stack.length > 0) {
                reversed += stack.pop();
            }
            reversed += " ";
        }
    }
    
    while (stack.length > 0) {
        reversed += stack.pop();
    }
    
    return reversed;
}

let input = "Hello World";
let output = reverseWithStack(input);
console.log(output);

olleH dlroW