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
}
​