Leetcode 202. happy number (2022.07.21)

Write an algorithm to judge a number n Is it a happy number .

「 Happy number 」 Defined as ：

For a positive integer , Replace the number with the sum of the squares of the numbers in each of its positions .
Then repeat the process until the number becomes 1, It could be Infinite loop But it doesn't change 1.
If this process The result is 1, So this number is the happy number .
If n yes Happy number Just go back to true ; No , Then return to false .

Example 1：

Input ：n = 19
Output ：true

explain ：

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

Example 2：

Input ：n = 2
Output ：false

Tips ：

1 <= n <= 2³¹ - 1

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/happy-number

Method 1 ： Fast and slow pointer method

C++ Submission ：

class Solution {
    
public:

    int bitSquareSum(int n){
    
        int sum = 0;
        while(n > 0){
    
            int bit = n%10;
            sum += bit*bit;
            n = n/10;
        }
        return sum;

    }
    bool isHappy(int n) {
    
        int slow = n,fast = n;
        do{
    
            slow = bitSquareSum(slow);
            fast = bitSquareSum(fast);
            fast = bitSquareSum(fast);
        } while(slow != fast);
        
        return slow == 1;
    }
};