Find first repeating character using JavaScript

We have an array of string / number literals that may/may not contain repeating characters. Our job is to write a function that takes in the array and returns the index of the first repeating character. If the array contains no repeating characters, we should return -1.

So, let’s write the code for this function. We will iterate over the array using a for loop and use a map to store distinct characters as key and their index as value, if during iteration we encounter a repeating key we return its index otherwise at the end of the loop we return -1.

The code for this will be −

Example

const arr = [12,4365,76,43,76,98,5,31,4];
const secondArr = [6,8,9,32,1,76,98,0,65,878,90];
const findRepeatingIndex = (arr) => {
   const map = {};
   for(let i = 0; i < arr.length; i++){
      if(map[arr[i]]){
         return map[arr[i]];
      }else{
         map[arr[i]] = i;
      }
   }
   return -1;
};
console.log(findRepeatingIndex(arr));
console.log(findRepeatingIndex(secondArr));

Output

The output in the console will be −

2
-1

AmitDiwan

Published on 20-Aug-2020 06:24:06

• Related Questions & Answers
• Finding first non-repeating character JavaScript
• Return index of first repeating character in a string - JavaScript
• Finding the first non-repeating character of a string in JavaScript
• First non-repeating character using one traversal of string in C++
• Find the first non-repeating character from a stream of characters in Python
• Finding the index of the first repeating character in a string in JavaScript
• How to find its first non-repeating character in a given string in android?
• Python program to Find the first non-repeating character from a stream of characters?
• Java program to Find the first non-repeating character from a stream of characters
• Find the last non repeating character in string in C++
• Find the first repeated character in a string using C++.
• Longest Repeating Character Replacement in C++
• Detecting the first non-repeating string in Array in JavaScript
• Find the first repeating element in an array of integers C++
• Repeating each character number of times their one based index in a string using JavaScript