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  <meta charset="utf-8">
  <title>Happy number — visited set</title>
</head>
<body>
  <h1>Happy number — visited set</h1>
  <p>Edit values in <code>tests</code>, then click <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 isHappySet(n) {
        if (n < 1) {
          return false;
        }
        var seen = {};
        while (n !== 1 && !seen[n]) {
          seen[n] = true;
          n = sumOfSquares(n);
        }
        return n === 1;
      }
      var tests = [19, 2, 1, 7];
      var lines = [];
      var i;
      for (i = 0; i < tests.length; i++) {
        var value = tests[i];
        var label = isHappySet(value) ? "happy" : "unhappy";
        lines.push(value + ": " + label);
      }
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
</body>
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JavaScript Happy Number — Visited Set (Try It)