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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Alphabet Pattern 21 - Try It (Half Height)</title>
</head>
<body>
  <h1>Diamond Alphabet &amp; Stars (Half Height)</h1>
  <p>Enter half height when prompted, then click Run.</p>
  <pre id="output" style="font-family: monospace; white-space: pre;"></pre>
  <script>
    let n = parseInt(prompt("Enter half height (like 5):"), 10);
    let result = "";
    if (!Number.isFinite(n)) {
      result = "Please enter a whole number.";
    } else {
      n = Math.max(1, Math.min(n, 26));
      const base = "A".charCodeAt(0);

      for (let i = 1; i <= n; i++) {
        const ch = String.fromCharCode(base + i - 1);
        let line = "";
        for (let j = 1; j < i * 2; j++) {
          line += (j % 2 === 0) ? "*" : ch;
        }
        result += line + "\n";
      }

      for (let i = n - 1; i >= 1; i--) {
        const ch = String.fromCharCode(base + i - 1);
        let line = "";
        for (let j = 1; j < i * 2; j++) {
          line += (j % 2 === 0) ? "*" : ch;
        }
        result += line + "\n";
      }
    }

    document.getElementById("output").textContent = result;
  </script>
</body>
</html>

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JavaScript Alphabet Pattern 21 (Try It - Half Height)