happyno.cpp

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

// Helper function to calculate the sum of squares of digits of a number
int sumOfSquares(int n) {
    int sum = 0;
    while (n > 0) {
        int digit = n % 10;
        sum += digit * digit;
        n /= 10;
    }
    return sum;
}

// Function to determine if a number is happy
bool isHappy(int n) {
    vector<int> seen;  // Vector to keep track of numbers we've already seen
    while (n != 1) {
        n = sumOfSquares(n);  // Replace n with the sum of squares of its digits
        
        // Check if the number has already been seen (cycle detection)
        for (int i = 0; i < seen.size(); i++) {
            if (seen[i] == n) {
                return false;  // If we encounter a number we've seen before, a cycle is detected
            }
        }

        // Add the current number to the seen vector
        seen.push_back(n);
    }
    return true;  // The number became 1, so it's a happy number
}

int main() {
    int n;
    cout << "Enter a number: ";
    cin >> n;

    if (isHappy(n)) {
        cout << n << " is a happy number!" << endl;
    } else {
        cout << n << " is not a happy number!" << endl;
    }

    return 0;
}