202. Happy Number #

题目 #

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 <= 2^31 - 1

代码 #

use std::collections::HashSet;
impl Solution {
    pub fn is_happy(n: i32) -> bool {
        let mut p = n;
        let mut set: HashSet<i32> = HashSet::new();
        set.insert(p);

        loop {
            let mut sum = 0;
            while p > 0 {
                let z = p.rem_euclid(10);
                sum += z * z;
                p = p / 10;
            }

            if sum == 1 {
                return true;
            }

            if set.contains(&sum) {
                break;
            }

            set.insert(sum);
            
            p = sum;
        }

        return false;
    }
}