/*****************************************************Happy Numbers*****************************************************/ /***************************************https://www.geeksforgeeks.org/happy-numbers/************************************/ /***********************************************************************************************************************/ /* A Happy Number n is defined by the following process. Starting with n, replace it with the sum of the squares of its digits, and repeat the process until n equals 1, or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are Happy Numbers, while those that do not end in 1 are unhappy numbers. First few happy numbers are 1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49, 68, 70, 79, 82, 86, 91, 94, 97, 100 Examples: Input : 23 Output : Yes Explanation : First Iteration: 22 + 32 = 4 + 9 = 13 Second Iteration: 12 + 32 = 1 + 9 = 10 Third Iteration: 12 + 02 = 1 + 0 = 1 Since we reach 1, 23 is Happy. */ #include using namespace std; // Returns sum of squares of digits // of a number n. For example for n = 12 // it returns 1 + 4 = 5 int sumDigitSquare(int n) { int sq = 0; while (n) { int digit = n % 10; sq += digit * digit; n = n / 10; } return sq; } // Returns true if n is Happy number // else returns false. bool isHappy(int n) { // A set to store numbers during // repeated square sum process set s; s.insert(n); // Keep replacing n with sum of // squares of digits until we either // reach 1 or we endup in a cycle while (1) { // Number is Happy if we reach 1 if (n == 1) return true; // Replace n with sum of squares // of digits n = sumDigitSquare(n); // If n is already visited, a cycle // is formed, means not Happy if (s.find(n) != s.end()) return false; // Mark n as visited s.insert(n); } return false; } // Driver code int main() { int n; cout << "Enter a number: " << endl; cin >> n; string happy = isHappy(n) ? "" : " NOT"; cout << n << " is" << happy << " a happy number" << endl; return 0; }

[C++] Happy Numbers