Happy_Number.cpp

#include <bits/stdc++.h> 
using namespace std; 
  
int sumDigitSquare(int n) 
{ 
    int sq = 0; 
    while (n) { 
        int digit = n % 10; 
        sq += digit * digit; 
        n = n / 10; 
    } 
    return sq; 
} 
  
bool isHappy(int n) 
{ 
    set<int> s; 
    s.insert(n); 
  
    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; 
} 
  
int main() 
{ 
    int n = 23; 
    if (isHappy(n)) 
        cout << "Yes" << endl; 
    else
        cout << "No" << endl; 
    return 0; 
}