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  <meta charset="utf-8">
  <title>Happy number — Floyd</title>
</head>
<body>
  <h1>Happy number check (Floyd)</h1>
  <p>Edit <code>number</code>, then <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function sumOfSquares(n) {
        var total = 0;
        while (n > 0) {
          var digit = n % 10;
          total += digit * digit;
          n = Math.floor(n / 10);
        }
        return total;
      }
      function isHappy(n) {
        var slow = n;
        var fast = n;
        while (true) {
          slow = sumOfSquares(slow);
          fast = sumOfSquares(sumOfSquares(fast));
          if (slow === fast) {
            break;
          }
        }
        return slow === 1;
      }
      var number = 19;
      var msg =
        number < 1
          ? "Use a positive integer."
          : isHappy(number)
          ? number + " is a Happy Number."
          : number + " is not a Happy Number.";
      document.getElementById("out").textContent = msg;
    })();
  </script>
</body>
</html>

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JavaScript Happy Number — Floyd Check (Try It)