LeetCode 202. Happy Number

Write an algorithm to determine if a number 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, and 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 numbers.

Example: 19 is a happy number

• 1² + 9² = 82
• 8² + 2² = 68
• 6² + 8² = 100
• 1² + 0² + 0² = 1

O(n) memory complexity solution has nothing special. Just read the problem carefully.....

class Solution {private:     set<int> integers;public:   static int sumOfDigit(int n) {        int sum = 0;        while(n) {            int tmp = n % 10;            sum += tmp * tmp;            n = n / 10;        }        return sum;    }    bool isHappy(int n) {        int sum = sumOfDigit(n);        if(sum == 1) return true;        else {            if(integers.find(sum) != integers.end()) return false;            integers.insert(sum);            return isHappy(sum);        }    }};