LeetCode 202. Happy Number

 202. Happy Number

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

	class Solution {
	public:
	int getNext(int x){
	int res = 0;
	while(x > 0){
	res += (x % 10) * (x % 10);
	x /= 10;
	}
	return res;
	}
	bool isHappy(int n) {
	int slow = n;
	int fast = getNext(n);
	while(fast != 1 and slow != fast){
	slow = getNext(slow);
	fast = getNext(getNext(fast));
	}
	return fast == 1;
	}
	};

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