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Grokking the Coding Interview Patterns in JavaScript

First Unique Character in a String

Explore the problem of finding the first unique character in a string by tracking element occurrences. Learn to return the correct index or -1 if none exists, applying coding interview strategies with JavaScript.

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Statement

For a given string of characters, s, your task is to find the first non-repeating character and return its index. Return −1-1 if there’s no unique character in the given string.

Constraints:

  • 1≤1 \leq s.length ≤103\leq 10^{3}

  • Only lowercase English letters are accepted.

  • There are no spaces in the string.

Examples

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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

First Unique Character in a String

1.

What is the correct answer if the following string is given as input?

s = “awsjawuh”

A.

2

B.

4

C.

3

D.

6

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4
5

Try it yourself

Implement your solution in the following coding playground.

JavaScript
usercode > main.js
function firstUniqueChar(s){



    // Replace this placeholder return statement with your code

    return -1

}



export { firstUniqueChar };
First Unique Character in a String