First Non Repeating Character Using Hash in DSA C - Build from Scratch

First Non Repeating Character Using Hash

📖 Scenario: Imagine you are building a simple text analyzer that finds the first character in a word that does not repeat. This can help in games like word puzzles or in text processing tools.

🎯 Goal: You will write a C program that finds the first non-repeating character in a given string using a hash (array) to count character occurrences.

📋 What You'll Learn

Create a character array called input with the exact value "swiss"

Create an integer array called count of size 256 initialized to 0

Use a for loop with variable i to count occurrences of each character in input

Use a for loop with variable i to find the first character with count 1

Print the first non-repeating character using printf

💡 Why This Matters

🌍 Real World

Finding the first non-repeating character is useful in text analysis, spell checking, and game development.

💼 Career

This technique helps in coding interviews and software development tasks involving string processing and hashing.

1

Create the input string

Create a character array called input and set it to the exact string "swiss"

DSA C

# Your code here

Hint

Use char input[] = "swiss"; to create the string.

2

Create and initialize the count array

Add an integer array called count of size 256 and initialize all elements to 0

DSA C

#include 

int main() {
    char input[] = "swiss";
    int count[256] = {0};
    // Your code here
    return 0;
}

Hint

Use int count[256] = {0}; to create and initialize the array.

3

Count character occurrences

Use a for loop with variable i to iterate over input until the null character '\0' and increment count[input[i]] for each character

DSA C

#include 

int main() {
    char input[] = "swiss";
    int count[256] = {0};

    // Count characters
    // Your code here

    return 0;
}

Hint

Use a for loop to go through each character until '\0' and increase the count for that character.

4

Find and print the first non-repeating character

Use a for loop with variable i to iterate over input until '\0'. Inside the loop, check if count[input[i]] is 1. If yes, print the character using printf("%c\n", input[i]) and break the loop.

DSA C

#include 

int main() {
    char input[] = "swiss";
    int count[256] = {0};

    for (int i = 0; input[i] != '\0'; i++) {
        count[(unsigned char)input[i]]++;
    }

    // Find and print first non-repeating character
    // Your code here

    return 0;
}

Hint

Loop again through input and print the first character whose count is 1.