TheAlgorithms · AzadN · Nov 4, 2020 · Nov 4, 2020 · Nov 4, 2020 · Nov 4, 2020
@@ -0,0 +1,30 @@
+package Maths;
+
+public class HappyNumber {
+
+  // Check if a number is happy or not. Refer : https://mathworld.wolfram.com/HappyNumber.html
+  public static boolean isHappy(int num) {
+    int slow = num, fast = num;
+    do {
+      slow = digitSquareSum(slow); // Move one step
+      fast = digitSquareSum(digitSquareSum(fast)); // Move 2 steps
+    } while (slow != fast);
+    return slow == 1; // See if the cycle is stuck on number 1
+  }
+
+  public static int digitSquareSum(int num) {
+    int sum = 0, digit;
+    while (num > 0) {
+      digit = num % 10;
+      sum += digit * digit;
+      num /= 10;
+    }
+    return sum;
+  }
+
+  public static void main(String[] args) {
+    // Testcases
+    assert isHappy(23);
+    assert !isHappy(11);
+  }
+}