Count all contiguous substrings of string S where the first and last characters are the same. (USING RECURSION in C++)

#include <iostream>

using namespace std;

// Count how many times it starts and ends with same string

int go(string str, int i, int j, int n) {

    if(n == 1) {

        return 1;

    }

    

    if(n<=0) {

        return 0;

    }

    

    int res = go(str, i+1, j, n-1)+go(str, i, j-1, n-1)-go(str, i+1, j-1, n-2);

    

    if(str[i] == str[j]) {

        res++;

    }

    

    return res;

}

int main() {

    string S = "abcab";

    int size = S.length();

    

    cout << go(S, 0, size-1, size);

    

    

    return 0;

}

OUTPUT:

7

Student Info Display (University OOPs Lab Topic)

 #include <iostream>

using namespace std;

// Base class

class Person {

protected: 

    string name;

    int age;

public:

    // Parameterized constructor

    Person(string n, int a) {

        name = n;

        age = a;

        cout << "Person constructor called with name = " << name << " and age = " << age << endl;

    }

};

// Derived class

class Student : public Person {

private: 

    string studentID;

    

public:

    // COnstructor for Student that intializes base class (Person) and studentID

    Student(string n, int a, string id) : Person(n, a), // Call the base class constructor with name and age

    studentID(id) {

        

        // Constructor body (can be empty if no additional initialization is needed)

    } 

    

    

    // Method to display student info

    void displayStudentInfo() {

        cout << "Name: " << name << endl;

        cout << "Age: " << age << endl;

        cout << "Student ID: " << studentID << endl;

    }

};

int main() {

    Student student("Rahul", 20, "50342324");

    student.displayStudentInfo();

    return 0;

}

Find all Occurences using Recursion in C++

 #include <iostream>

using namespace std;

void allOccurences(int arr[], int key, int i, int n) {

    if(i == n) {

        return;

    }

    

    if(arr[i] == key) {

        cout << i << " ";

    }

    

    allOccurences(arr, key, i+1, n);

}

int main() {

    int arr[] = {3, 2, 4, 5, 6, 2, 7, 2, 2};

    int n = sizeof(arr)/sizeof(int);

    int key = 2; 

    allOccurences(arr, key, 0, n);

    return 0;

}

Bank Account Question (University OOPs Lab Topic)

 #include <iostream>

using namespace std;

class BankAccount {

private:

    int accountNumber;

    double balance;

   

public:    

// Constructor to initialize account    

    BankAccount(int accNo, double initialBalance = 0.0) {

        accountNumber = accNo;

        balance = initialBalance;

    }

   

   

    void deposit(double amount) {

        if(amount > 0) {

            balance += amount;

             cout << "Deposited: " << amount << endl;

        } else {

            cout << "Invalid deposit amount!" << endl;

        }

    }

    void withdraw(double amount) {

        if(amount > 0 && amount <= balance) {

            balance -= amount;

            cout << "Withdrawn: " << amount<< endl;

        } else {

            cout << "Invalid or insufficient funds for withdrawal!" << endl;

        }

    }

   

    // method to get balance

    double getBalance() const {

        return balance;

    }

   

    // Optional: Show account number and balance

    void showAccountInfo() const {

        cout << "Account Number: " << accountNumber << endl;

        cout << "Current Balance: " << balance << endl;

    }

   

   

};

int main() {

    // Create a bank with account number 1001 and initial balance of 500

   

    BankAccount account(1001, 500.0);

   

    account.showAccountInfo();

   

    // Perform deposit and withdrawal operations

    account.deposit(250);

    account.withdraw(100);

   

    //Show final balance

    cout << "Final balance: " << account.getBalance() << endl;

   

    return 0;

}

Function Pointer (the TOPIC that I missed!) - Part 1

 #include <iostream>

using namespace std;

// Function declaration + definition (function to be pointed to..)

void greet() {

    cout << "Hello!\n";

}

int main() {

    

    // Function pointer

    void (*fp)();

    // Assign the address of greet() fnx to the fnx pointer..

    

    fp = greet;

    

    greet();

    

    return 0;

}

OR

with parameters 

#include <iostream>

using namespace std;

int add(int a, int b) {

    return a+b;

}

int main() {

    // Declare function pointer

    int (*operation)(int, int);

    

    

    // Assign fnx address

    operation = add;

    

    // Call the fnx using pointer

    cout << operation(4, 4);

    return 0;

}

Watermelon in Codeforces(It accepted at 3rd attempt!!)

 #include <iostream>

using namespace std;

int main() {

    int watermelon;

    cin >> watermelon;

    

    if(watermelon == 2) {

        cout << "NO" << endl;

    }

    else if(watermelon%2==0) { // even no;

        cout << "YES" << endl;

    }else { // odd no.

        cout << "NO" << endl;

    }

    

    return 0;

}

Binary Strings using Recursion in C++

 #include <iostream>

#include <string>

using namespace std;

void binString(int n, int lastPlace, string ans) {

    if(n == 0) {

        cout << ans << endl;

        return;

    }

   

    if(lastPlace != 1) {

        binString(n-1, 0, ans+'0');

        binString(n-1, 1, ans+'1');

    } else {

        binString(n-1, 0, ans + '0');

    }

}

void binString(int n, string ans) {

    if(n == 0) {

        cout << ans << endl;

        return;

    }

   

    if(ans[ans.size()-1] != '1') {

        binString(n-1, ans+'0');

        binString(n-1, ans+'1');

    } else {

        binString(n-1, ans + '0');

    }

}

int main() {

    string ans = " ";

    binString(3, ans);

return 0;

}