JavaScript Program to Find the First Repeated Word in String
Given a string, our task is to find the 1st repeated word in a string.
Examples:
Input: “Ravi had been saying that he had been there”
Output: had
Input: “Ravi had been saying that”
Output: No Repetition
Below are the approaches to Finding the first repeated word in a string:
Table of Content
- Using Set
- Using indexOf method
- Using Nested for loop
- Using a Map
- Using an Object
Using Set
- In this approach, we are using a Set data structure to track unique words encountered during iteration over the input string.
- If a word is already in the set, it’s identified as the first repeated word; otherwise, the result remains “No Repetition”.
Example: The below example uses Set to Find the first repeated word in a string.
let str = "GFG had been saying that he had been there";
let words = str.split(" ");
let wSet = new Set();
let res = "No Repetition";
for (let word of words) {
if (wSet.has(word)) {
res = word;
break;
} else {
wSet.add(word);
}
}
console.log(res);
Output:
had
Time Complexity: O(n), where n is the number of words in the input.
Space Complexity: O(n)
Using indexOf method
- In this approach, we are using the indexOf method to check if the current word appears again later in the array of words.
- If it does, the word is identified as the first repeated word; otherwise, the result remains “No Repetition”.
Example: The below example uses indexOf to Find the first repeated word in a string.
let str = "Ravi had been saying that he been there";
let words = str.split(" ");
let res = "No Repetition";
for (let i = 0; i < words.length; i++) {
if (words.indexOf(words[i]) !== i) {
res = words[i];
break;
}
}
console.log(res);
Output:
been
Time Complexity: O(n^2), where n is the number of words in the input.
Space Complexity: O(1)
Using Nested for loop
- In this approach we splits the input sentence into an array of words and then uses nested for loop to compare each word with every other word that comes after it.
- If a match is found we will return that word as the first repeated word.
Example: The below example uses nested for loop to Find the first repeated word in a string.
function findFirstRepeatedWord(sentence) {
const words = sentence.split(' ');
for (let i = 0; i < words.length; i++) {
for (let j = i + 1; j < words.length; j++) {
if (words[i] === words[j]) {
return words[i];
}
}
}
return null;
}
const sentence = "Ravi had been saying that he had been there";
const repeatedWord = findFirstRepeatedWord(sentence);
console.log(repeatedWord);
Output
had
Time Complexity: O(n^2), where n is the number of words in the input.
Space Complexity: O(1)
Using a Map
In this approach we use map to track the frequency of each word. we iterate over each word in the array of words. For each word, it checks if map already has the word using Map.has(). if the word is found we will return it, otherwise we add it to the map sing Map.set().
Example: The below example uses map to find the first Repeated Word in String.
function findFirstRepeatedWord(str) {
const words = str.toLowerCase().split(' ');
const wordMap = new Map();
for (let word of words) {
if (wordMap.has(word)) {
return word;
} else {
wordMap.set(word, 1);
}
}
return null;
}
const str = "GFG had been saying that he had been there";
const repeatedWord = findFirstRepeatedWord(str);
console.log(repeatedWord);
Output
had
Using an Object
In this approach, we use an object to track the frequency of each word. We iterate over each word in the array of words. For each word, we check if the object already has the word as a key. If the word is found, we return it as the first repeated word. Otherwise, we add it to the object with a count.
Example: The below example uses an object to find the first repeated word in a string.
function findFirstRepeatedWord(str) {
const words = str.split(' ');
const wordCount = {};
for (let word of words) {
if (wordCount[word]) {
return word;
} else {
wordCount[word] = 1;
}
}
return "No Repetition";
}
const str = "Ravi had been saying that he had been there";
const repeatedWord = findFirstRepeatedWord(str);
console.log(repeatedWord);
Output
had
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