202. Happy Number

Problem Statement

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

Solution:

Rust

impl Solution {
    pub fn is_happy(n: i32) -> bool {
        let (mut slow, mut fast) = (n, n);

        loop {
            slow = Self::sum_of_squares(slow);
            fast = Self::sum_of_squares(Self::sum_of_squares(fast));

            if slow == 1 || fast == 1 {
                return true;
            }

            // Floyd's cycle detection
            if slow == fast {
                return false;
            }
        }
    }

    pub fn sum_of_squares(mut num: i32) -> i32 {
        let mut sum = 0;

        while num > 0 {
            let digit = num % 10;
            sum += digit * digit;
            num /= 10;
        }

        sum
    }
}

202. Happy Number #

Problem Statement #

Solution: #

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202. Happy Number

Problem Statement

Solution:

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