【easy】202. Happy Number

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

//写的不对……没有想到用set……问题在于不是1的循环，那样的话就不是一个循环数1，而是一个循环节，要判断之前的数有没有出现
class Solution {
public:
    bool isHappy(int n) {
        if (n < 1)
            return false;
        if (n == 1)
            return true;
        unordered_set<int> showedNums;
        showedNums.insert(n);

        while (true) {
            int s = 0;
            while (n) {
                s += (n % 10) * (n % 10);
                n = n / 10;
            }

            if (s == 1)
                return true;
            else if (showedNums.find(s) != showedNums.end())
                return false;
            n = s;
            showedNums.insert(s);
        }
    }
};