solve 202.happy-number

Author: andavid

vscode/202.happy-number.java

@@ -0,0 +1,55 @@
+/*
+ * @lc app=leetcode id=202 lang=java
+ *
+ * [202] Happy Number
+ *
+ * https://leetcode.com/problems/happy-number/description/
+ *
+ * algorithms
+ * Easy (46.28%)
+ * Likes:    998
+ * Dislikes: 264
+ * Total Accepted:    260.4K
+ * Total Submissions: 561.6K
+ * Testcase Example:  '19'
+ *
+ * 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:
+ * 1^2 + 9^2 = 82
+ * 8^2 + 2^2 = 68
+ * 6^2 + 8^2 = 100
+ * 1^2 + 0^2 + 0^2 = 1
+ *
+ */
+class Solution {
+  public boolean isHappy(int n) {
+    Set<Integer> set = new HashSet<>();
+    while (n != 1 && !set.contains(n)) {
+      set.add(n);
+      n = sumOfDigits(n);
+    }
+    return (n == 1) ? true : false;
+  }
+
+  public int sumOfDigits(int n) {
+    int sum = 0;
+    while (n != 0) {
+      sum += (n%10) * (n%10);
+      n /= 10;
+    }
+    return sum;
+  }
+}
+