202. Happy Number

Easy (Dễ) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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

💻 Lời Giải

C++ 0202-happy-number.cpp 
class Solution {
public:
    int splitDigit(int n) {
        int s = 0;
        while (n > 0) {
            int t = n % 10;
            s += t * t;
            n /= 10;
        }
        return s;
    }
    bool isHappy(int n) {
        int slow = n, fast = n;
        do {
            slow = splitDigit(slow);
            fast = splitDigit(fast);
            fast = splitDigit(fast);
        } while (slow != fast);
        return fast == 1;
    }
};