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Solve LeetCode 3 Longest Substring Without Repeating Characters in C++ using the sliding window

Longest Substring Without Repeating Characters in C++ LeetCode 3 · sliding window · last index array Table of Contents Problem Statement Approach Algorithm C++ Program Input Sample Output Output Explanation Dry Run Flow of Execution Time Complexity Space Complexity Applications Key Points Interview Questions Frequently Asked Questions Conclusion Problem Statement 3. Longest Substring Without Repeating Characters Given a string s , find the length of the longest substring that contains no repeating characters. A substring is a continuous part of the string, so "pwke" is a subsequence of "pwwkew" but not a substring. Approach We use a sliding window . The window is the part of the string between start and end , and we always keep it free of repeated characters. An array lastIndex of size 128 remembers the most recent position of every ASCII ...
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Reverse a String in C

Reverse String in C

Reverse a String in C

This C program reverses a given string using a simple two-pointer technique. It swaps characters from both ends until the middle is reached.

✅ C Program Code:


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

void reverse(char str[])
{
    int start = 0;
    int end = strlen(str) - 1;
    int temp;
    while (start < end)
    {
        temp = str[start];
        str[start] = str[end];
        str[end] = temp;
        start++;
        end--;
    }
}

int main()
{
    char str[100];
    printf("Enter the string:\n");
    scanf("%[^\n]", str);
    printf("Before reversing the string: %s\n", str);
    reverse(str);
    printf("After reversing the string: %s", str);
}

📌 How It Works:

  • reverse(): Swaps characters from start and end using a while loop until the full string is reversed.
  • scanf("%[^\n]", str): Reads a line of input including spaces.
  • main(): Takes user input, prints original and reversed string.

💻 Sample Output:

Enter the string:
Hello World
Before reversing the string: Hello World
After reversing the string: dlroW olleH

🔍 Keywords:

reverse string in C, string handling in C, two-pointer approach C, beginner string program, C logic examples, character array reverse

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