happynumber.cpp

/*Write an algorithm to determine if a number n is happy.

A happy number is a number defined by the following process:

Starting with any positive integer, replace the number by the sum of the squares of its digits.
Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
Those numbers for which this process ends in 1 are happy.
Return true if n is a happy number, and false if not.

 

Example 1:

Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:

Input: n = 2
Output: false
 

Constraints:

1 <= n <= 231 - 1
*/
#include <bits/stdc++.h> 
using namespace std;

class Solution {
    private:  int numSquareSum(int n)
{
    int squareSum = 0;
    while (n) {
        squareSum += (n % 10) * (n % 10);
        n /= 10;
    }
    return squareSum;
}
public:
    bool isHappy(int n) {
        set<int> st;
    while (1)
    {
        n = numSquareSum(n);
        if (n == 1)
            return true;
        if (st.find(n) != st.end())
            return false;
        st.insert(n);
    }
    }
};