JavaScript Program to Print All Duplicate Characters in a String
Last Updated :
17 Jun, 2024
In this article, we will learn how to print all duplicate characters in a string in JavaScript. Given a string S, the task is to print all the duplicate characters with their occurrences in the given string.
Example:
Input: S = “geeksforgeeks”
Output:
e, count = 4
g, count = 2
k, count = 2
s, count = 2
Examples of Print All Duplicate Characters in a String In JavaScript
1. Using For Loop in JavaScript
In this approach, an object named charCount to effectively maintain the frequency of characters in the string. It sequentially processes each character in the input string, increasing its count in the charCount object. Once the character frequencies are established, the code then traverses through the charCount object. It selectively prints characters that have occurrences greater than one, thereby accurately showcasing the duplicate characters along with the corresponding count of duplications.
Example: In this example, we are using a for loop.
JavaScript
function printDups(str) {
let charCount = {};
for (let i = 0; i < str.length; i++) {
let character = str[i];
charCount[character] =
(charCount[character] || 0) + 1;
}
for (let char in charCount) {
if (charCount[char] > 1) {
console.log(
char +
", count = " +
charCount[char]
);
}
}
}
let str = "geeksforgeeks";
printDups(str);
Outputg, count = 2
e, count = 4
k, count = 2
s, count = 2
2. Using Sorting in JavaScript
- Sort the given string.
- Loop through the sorted string to find the duplicates.
- If the next character is the same as the current character then we keep on counting the occurrence of that char.
- If the count is greater than one then we print the character and its count.
Example: In this example we are using Sorting
JavaScript
function printDuplicates(str) {
let len = str.length;
// Sorting the string
str = str.split('').sort().join('');
// Loop through the sorted string to find duplicates
for (let i = 0; i < len; i++) {
let count = 1;
// Counting the occurrences of each character
while (i < len - 1 && str[i] == str[i + 1]) {
count++;
i++;
}
// Printing the duplicate character and its count
if (count > 1) {
console.log(str[i] + ", count = " + count);
}
}
}
let str = "geeksforgeeks";
printDuplicates(str);
Outpute, count = 4
g, count = 2
k, count = 2
s, count = 2
3. Using Hashing in JavaScript
- Declare a unordered map of the char-int pair.
- Traverse the string using a loop and increase the count of the present char in the map.
- Iterate through the map and print a character that has a value greater than one in map.
Example: In this example we are using Hashing.
JavaScript
// JavaScript program to count all duplicates
// from string using maps
function printDups(str) {
let count = new Map();
for (let i = 0; i < str.length; i++) {
if (count.has(str[i])) {
count.set(
str[i],
count.get(str[i]) + 1
);
} else {
count.set(str[i], 1);
}
//increase the count of characters by 1
}
//iterating through the unordered map
for (let [it, it2] of count) {
if (it2 > 1)
//if the count of characters is
//greater than 1 then duplicate found
console.log(it, ", count = ", it2);
}
}
/* Driver code*/
let str = "geeksforgeeks";
printDups(str);
Outputg , count = 2
e , count = 4
k , count = 2
s , count = 2
4. Using Set()
This approach uses two Sets to track characters in a string, seen set to store characters encountered, and duplicates set to store duplicate characters. It iterates over the string, adding characters to seen if they are not already there, or to duplicates if they are.
Example: In this example we are using Set().
JavaScript
function findDuplicates(str) {
const seen = new Set();
const duplicates = new Set();
for (let char of str) {
if (seen.has(char)) {
duplicates.add(char);
} else {
seen.add(char);
}
}
duplicates.forEach(char => {
const count = str.split(char).length - 1;
console.log(`${char}, count= ${count}`);
});
}
const str = "geeksforgeeks";
findDuplicates(str);
Outpute, count= 4
g, count= 2
k, count= 2
s, count= 2
5. Using Reduce Method in JavaScript
In this approach, we will use the reduce method to create an object that tracks the count of each character. Then, we will loop through this object to identify and print characters that have a count greater than one.
Example: Using the reduce Method
JavaScript
function printDupsUsingReduce(str) {
// Using reduce to build the character count object
let charCount = str.split('').reduce((acc, char) => {
acc[char] = (acc[char] || 0) + 1;
return acc;
}, {});
// Iterating over the charCount object to print duplicates
Object.keys(charCount).forEach(char => {
if (charCount[char] > 1) {
console.log(`${char}, count = ${charCount[char]}`);
}
});
}
let str = "geeksforgeeks";
printDupsUsingReduce(str);
Outputg, count = 2
e, count = 4
k, count = 2
s, count = 2
6. Using Filter Method in JavaScript
In this approach, we will use the filter method to identify characters that appear more than once in the string. This method will first create an array of characters from the string, then filter out the characters that appear only once, and finally count the occurrences of each duplicate character.
Example: Using the Filter Method
JavaScript
function printDupsUsingFilter(str) {
// Convert string to an array of characters
let chars = str.split('');
// Filter characters that appear more than once
let duplicates = chars.filter((char, index, arr) => arr.indexOf(char) !== arr.lastIndexOf(char));
// Create a set to get unique duplicate characters
let uniqueDups = new Set(duplicates);
// Count and print each unique duplicate character
uniqueDups.forEach(char => {
const count = str.split(char).length - 1;
console.log(`${char}, count = ${count}`);
});
}
let str = "geeksforgeeks";
printDupsUsingFilter(str);
Outputg, count = 2
e, count = 4
k, count = 2
s, count = 2
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