Find the Index of the First Occurrence in a String In C,CPP,JAVA,PYTHON,C#,JS

Problem Statement:

Given a string s and a target character ch, your task is to find the index of the first occurrence of the character ch in the string s. If the character is not found, return -1.

Input:

• A string s of length n (1 ≤ n ≤ 10^5).
• A character ch which is present in the string.

Output:

• The index of the first occurrence of the character ch in the string s.
• If the character is not found, return -1.

Example:

Example 1:

Input: s = "hello", ch = 'e'
Output: 1
Explanation: The first occurrence of 'e' is at index 1.

Example 2:

Input: s = "hello", ch = 'a'
Output: -1
Explanation: 'a' is not present in the string.

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Approach:

To solve the problem, we can use a linear scan of the string s to look for the character ch. The first occurrence of ch in the string will be returned as the index. If no match is found, return -1.

• Step 1: Iterate through the string.
• Step 2: Check each character to see if it matches ch.
• Step 3: If a match is found, return the current index.
• Step 4: If the loop completes without finding the character, return -1.

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Algorithm:

1. Loop through each character of the string s from index 0 to n-1.
2. For each character at index i, check if it is equal to ch.
3. If a match is found, return the index i.
4. If the loop finishes without finding the character, return -1.

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Code Implementation:

C:

#include <stdio.h>
#include <string.h>

int first_occurrence(char* s, char ch) {
    for (int i = 0; i < strlen(s); i++) {
        if (s[i] == ch) {
            return i;
        }
    }
    return -1;
}

int main() {
    char s[] = "hello";
    char ch = 'e';
    int result = first_occurrence(s, ch);
    printf("%d\n", result);  // Output: 1
    return 0;
}

C++:

#include <iostream>
#include <string>
using namespace std;

int first_occurrence(string s, char ch) {
    for (int i = 0; i < s.length(); i++) {
        if (s[i] == ch) {
            return i;
        }
    }
    return -1;
}

int main() {
    string s = "hello";
    char ch = 'e';
    cout << first_occurrence(s, ch) << endl;  // Output: 1
    return 0;
}

Java:

public class Main {
    public static int firstOccurrence(String s, char ch) {
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == ch) {
                return i;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        String s = "hello";
        char ch = 'e';
        System.out.println(firstOccurrence(s, ch));  // Output: 1
    }
}

Python:

def first_occurrence(s, ch):
    for i in range(len(s)):
        if s[i] == ch:
            return i
    return -1

s = "hello"
ch = 'e'
print(first_occurrence(s, ch))  # Output: 1

C#:

using System;

class Program {
    static int FirstOccurrence(string s, char ch) {
        for (int i = 0; i < s.Length; i++) {
            if (s[i] == ch) {
                return i;
            }
        }
        return -1;
    }

    static void Main() {
        string s = "hello";
        char ch = 'e';
        Console.WriteLine(FirstOccurrence(s, ch));  // Output: 1
    }
}

JavaScript:

function firstOccurrence(s, ch) {
    for (let i = 0; i < s.length; i++) {
        if (s[i] === ch) {
            return i;
        }
    }
    return -1;
}

let s = "hello";
let ch = 'e';
console.log(firstOccurrence(s, ch));  // Output: 1

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Time Complexity:

• The algorithm loops through the string once, checking each character.
• Time Complexity: O(n), where n is the length of the string s.

Space Complexity:

• The space complexity is O(1) since we are not using any additional data structures that depend on the size of the input.

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Edge Cases:

1. Character not found: If the character ch is not in the string, the function should return -1.
2. Empty string: If the string is empty, the function should return -1 as there is no character to search.
3. Single character string: If the string consists of only one character, it should return 0 if the character matches.