DSA - Data Structures and Algorithms

• 1 August 2025 String Manipulation
  • Reverse a String
    • 2 pointers: Start and End or Left and Right
    • Algorithm:
      1. Initialize two pointers: one at the start and one at the end of the list. Start=0 and End=len(string)-1
      2. Repeat until start < end. Swap the character of start and end. Increment start, decrement end.
      3. After loop ends, string is reversed.
      4. Return or print the reversed string.
    • Time Complexity: O(n)
  • Check if a String is a Palindrome
    • A palindrome is a string that reads the same backward as forward (e.g., "madam", "racecar").
    • Algorithm:
      1. Reverse the string.
      2. Compare the original string with its reversed version.
      3. If both are equal, the string is a palindrome; otherwise, it is not.
    • Time Complexity: O(n)
  • Count Vowels and Consonants
    • Iterate through each character in the string.
    • Use a counter for vowels and another for consonants.
    • Algorithm:
      1. Initialize two counters: vowels = 0, consonants = 0.
      2. Loop through each character in the string.
      3. For each character, check if it is a letter.
      4. If the letter is a vowel (a, e, i, o, u, A, E, I, O, U), increment vowels.
      5. If the letter is a consonant, increment consonants.
      6. Return or print the counts of vowels and consonants.
    • Time Complexity: O(n) n=length of the string
  • Find the First Non-Repeating Character
    • Identifies the first character in a string that does not repeat.
    • Algorithm:
      1. Traverse the string to count occurrences of each character.
      2. Iterate again to find the first character with a count of one.
    • Time Complexity: O(n)
  • Anagram Check
    • Determines if two strings are anagrams (contain the same characters in any order).
    • Algorithm:
      1. Sort both strings and compare, or count character frequencies and compare.
    • Time Complexity: O(n)
  • String Compression
    • Compresses a string by replacing sequences of the same character with the character followed by the count.
    • Algorithm:
      1. Iterate through the string, count consecutive characters, and build the compressed string.
    • Time Complexity: O(n)
  • Longest Substring Without Repeating Characters
    • Finds the length of the longest substring without repeating characters.
    • Algorithm:
      1. Use a sliding window with a hash set to track unique characters.
    • Time Complexity: O(n)
  • Capitalize First Letter Each Word In a String
    • Capitalizes the first letter of each word in a given string.
    • Algorithm:
      1. Split the string into words, capitalize the first letter of each, and join them back.
    • Time Complexity: O(n)
• 4 August 2025 5 August 2025 Array Manipulation