Leetcode - Happy Number
https://leetcode.com/problems/happy-number/
Write an algorithm to determine if a number 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, and 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 numbers.
Example:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
There are several conditions in the end.
1. sum equal to 1
2. sum repeat in a loop
3. sum goes infinity
Use a hash to track every round of sum and see whether it occurs before, if so, return false
func isHappy(n int) bool {
hash := map[int]bool{}
for n != 1 && !hash[n] {
hash[n] = true
n = getNext(n)
}
return n == 1
}
func getNext(n int) int {
sum := 0
for n > 0 {
d := n%10
n /= 10
sum += d*d
}
return sum
}
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