Add 202

Author: ChienkuChen

src/_202/202.happy-number.java

@@ -0,0 +1,33 @@
+package _202;
+
+class Solution {
+    public boolean isHappy(int n) {
+        // because if it isn't a happy number, it loops endlessly in a cycle which does not include 1.
+        // I remind the algorithm of detecting a cycle
+
+        int slow = n;
+        int fast = n;
+
+        do {
+            slow = sum(slow);
+            fast = sum(sum(fast));
+        } while (slow != fast && slow != 1);
+
+        return slow == 1;
+    }
+
+    private int sum(int n) {
+        int sum = 0;
+        while (n > 0) {
+            sum += Math.pow(n % 10, 2);
+            n /= 10;
+        }
+
+        return sum;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new Solution().isHappy(19));
+        System.out.println(new Solution().isHappy(14));
+    }
+}