202. Happy Number

Easy

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

解題

Runtime: 0 ms, faster than 100.00%

Memory Usage: 2.2 MB, less than 29.6%

func isHappy(n int) bool {
    m := make(map[int]bool)

    for (n > 9 || newNum(n) > 9) && !m[n] {
        m[n] = true
        n = newNum(n)
    }

    return n == 1
}

func newNum(n int) int {
    res := 0
    mul := 1
    for n > 0 {
        res += (n % 10) * (n % 10)
        n = n / 10
        mul *= 10
    }

    return res
}