String Basic Questions

Convert to lowercase

char toLowerCase(char ch) {
    // Check if the character is already in lowercase
    if(ch >= 'a' && ch <= 'z')
        return ch; // If it's lowercase, return it as is.
    else {
        // Convert uppercase letter to lowercase
        char temp = ch - 'A' + 'a';
        return temp; // Return the lowercase version
    }
}

Example:

char ch1 = 'A';
char ch2 = 'm';
char ch3 = 'Z';

// Call the function for each character
char res1 = toLowerCase(ch1); // 'A' -> 'a'
char res2 = toLowerCase(ch2); // 'm' -> 'm' (already lowercase)
char res3 = toLowerCase(ch3); // 'Z' -> 'z'

Iterations:

1. For ch1 = 'A':
   • It is not lowercase ('A' < 'a').
   • Convert it: 'A' - 'A' + 'a' = 'a'.
   • Output: 'a'.
2. For ch2 = 'm':
   • It is already lowercase ('m' >= 'a' && 'm' <= 'z').
   • Return 'm' as is.
   • Output: 'm'.
3. For ch3 = 'Z':
   • It is not lowercase ('Z' < 'a').
   • Convert it: 'Z' - 'A' + 'a' = 'z'.
   • Output: 'z'.

Get Length of String

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

    return count;
}

Reverse String

void reverse(char name[], int n) {
    int s = 0; // Start pointer
    int e = n - 1; // End pointer

    // Continue swapping until the start pointer crosses the end pointer
    while (s < e) {
        swap(name[s++], name[e--]); // Swap and update pointers
    }
}

Example:

char name[] = "hello";
int n = 5; // Length of the string
reverse(name, n); // After reversing, name becomes "olleh"

Iterations:

1. Initial Array: ['h', 'e', 'l', 'l', 'o']
   • s = 0, e = 4
   • Swap name[0] (h) with name[4] (o).
   • Array after swap: ['o', 'e', 'l', 'l', 'h']
   • s becomes 1, e becomes 3.
2. Second Iteration:
   • s = 1, e = 3
   • Swap name[1] (e) with name[3] (l).
   • Array after swap: ['o', 'l', 'l', 'e', 'h']
   • s becomes 2, e becomes 2.
3. Termination:
   • s = 2, e = 2
   • Since s is no longer less than e, the loop terminates.
4. Final Output: The reversed array is: "olleh".

Check String is Palindrome or not

bool checkPalindrome(char a[], int n) {
    int s = 0;        // Start pointer
    int e = n - 1;    // End pointer
    // Loop until the pointers meet or cross each other
    while (s <= e) {
        // Convert characters to lowercase and compare them
        if (toLowerCase(a[s]) != toLowerCase(a[e])) {
            return 0;  // Return false if any mismatch is found
        } else {
            // Move both pointers towards the center
            s++;
            e--;
        }
    }
    // If the loop completes without mismatches, it's a palindrome
    return 1;  // Return true
}

Example:

char str[] = "Madam";
int n = 5; // Length of the string
bool result = checkPalindrome(str, n); // Result will be true (palindrome)

Iterations:

1. Initial String: "Madam"
   • Start pointer: s = 0, End pointer: e = 4\

Iterations:

1. Compare a[0] (‘M’) and a[4] (‘m’):
   • Convert both to lowercase: toLowerCase('M') = 'm' and toLowerCase('m') = 'm'.
   • Characters match → move s to 1 and e to 3.
2. Compare a[1] (‘a’) and a[3] (‘a’):
   • Convert both to lowercase: toLowerCase('a') = 'a' and toLowerCase('a') = 'a'.
   • Characters match → move s to 2 and e to 2.
3. Compare a[2] (‘d’) and a[2] (‘d’):
   • Convert both to lowercase: toLowerCase('d') = 'd'.
   • Characters match → pointers now meet at the center (s = 2, e = 2).

Since all characters match, the function will return true (1), indicating that the string is a palindrome.

Get Max occurrence character from string

char getMaxOccCharacter(string s) {
    int arr[26] = {0};  // Array to store the frequency of each character (26 lowercase letters)
    // Step 1: Count the occurrences of each character in the string
    for(int i = 0; i < s.length(); i++) {
        char ch = s[i];
        int number = ch - 'a';  // Convert the character to its index (0 for 'a', 1 for 'b', etc.)
        arr[number]++;  // Increment the frequency for that character
    }
    // Step 2: Find the character with the maximum occurrence
    int maxi = -1;  // Variable to store the maximum frequency found
    int ans = 0;    // Variable to store the index of the most frequent character
    for(int i = 0; i < 26; i++) {
        if(maxi < arr[i]) {
            ans = i;    // Update the index of the most frequent character
            maxi = arr[i];  // Update the maximum frequency value
        }
    }
    // Step 3: Convert the index back to the corresponding character and return it
    return 'a' + ans;  // Convert the index back to a character ('a' + 0 = 'a', 'a' + 1 = 'b', etc.)
}

Example:

string s = "character";
char result = getMaxOccCharacter(s);  // Result will be 'c'

1. Initial string: “character”

Step 1: Counting frequencies

• The frequency of each character in “character” is:
  • ‘c’: 2 occurrences
  • ‘h’: 1 occurrence
  • ‘a’: 2 occurrences
  • ‘r’: 2 occurrences
  • ‘t’: 1 occurrence
  • ‘e’: 1 occurrence Array after counting frequencies:

arr[] = {2, 0, 2, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0}
// Indices correspond to 'a' through 'z'

Step 2: Finding the maximum occurrence

• The function finds the maximum frequency is 2, which occurs at index 2 (for ‘c’).

Step 3: Returning the result

• The function returns ‘c’ as it is the most frequent character.

Output:

Result: 'c'