exercise(leetcode): 202

leetcode/202-happy-number/README.md

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+# 202. Happy number
+
+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`

leetcode/202-happy-number/solution.go

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+package main
+
+import (
+	"fmt"
+)
+
+func isHappy(n int) bool {
+	if n < 11 {
+		return n == 1 || n == 7 || n == 10
+	}
+
+	var number int
+	for n > 0 {
+		number += (n % 10) * (n % 10)
+		n /= 10
+	}
+
+	return isHappy(number)
+}
+
+func main() {
+	fmt.Println(isHappy(2))
+	fmt.Println(isHappy(7))
+	fmt.Println(isHappy(10))
+	fmt.Println(isHappy(19))
+}