Centered Alphabet Palindrome Pyramid (A, ABA, ABCBA, ...) in JavaScript

What You’ll Learn

Each row is a centered palindrome of letters: row 0 prints A, row 1 prints ABA, row 2 prints ABCBA, until the bottom row shows ABCDEDCBA for five rows. Leading spaces (rows - 1 - r) center the pyramid; ascend and descend loops mirror letters without duplicating the peak. Compare with Program 18 (left-aligned palindrome pyramid). Includes a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print a centered pyramid of rows lines. Row r prints (rows - 1 - r) leading spaces, then letters from A up to String.fromCharCode("A".charCodeAt(0) + r), then back down from peak - 1 to A.

// First 5 rows (centered)
    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

Inputs & Outputs

Minimal workflow

base = "A".charCodeAt(0)
for r from 0 to rows-1:
    append (rows-1-r) spaces
    peak = base + r
    for code from base to peak: append String.fromCharCode(code)
    for code from peak-1 down to base: append String.fromCharCode(code)
    console.log(line)

Approach comparison

🔮 Live Preview

Choose a row count between 1 and 26 and draw the centered alphabet palindrome pyramid in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs - fixed five rows with centering spaces and mirror loops, prompt input, and a left/right string-build variant for clarity. Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

let rows = 5;
rows = Math.max(1, Math.min(rows, 26));

const base = "A".charCodeAt(0);

for (let r = 0; r < rows; r++) {  // 0..4
  let line = "";

  // Centering spaces
  line += " ".repeat(rows - 1 - r);

  const peak = base + r;

  // Ascend: A..peak
  for (let code = base; code <= peak; code++) {
    line += String.fromCharCode(code);
  }

  // Descend: (peak-1)..A
  for (let code = peak - 1; code >= base; code--) {
    line += String.fromCharCode(code);
  }

  console.log(line);
}

    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

let rows = parseInt(prompt("Enter number of rows (max 26):"), 10);
if (!Number.isFinite(rows)) {
  console.log("Please enter a whole number.");
} else {
  rows = Math.max(1, Math.min(rows, 26));

  const base = "A".charCodeAt(0);

  for (let r = 0; r < rows; r++) {
    let line = "";
    line += " ".repeat(rows - 1 - r);
    const peak = base + r;
    for (let code = base; code <= peak; code++) {
      line += String.fromCharCode(code);
    }
    for (let code = peak - 1; code >= base; code--) {
      line += String.fromCharCode(code);
    }
    console.log(line);
  }
}

Enter number of rows (max 26): 3
  A
 ABA
ABCBA

let rows = 5;
rows = Math.max(1, Math.min(rows, 26));

const base = "A".charCodeAt(0);

for (let r = 0; r < rows; r++) {
  const peak = base + r;
  let left = "";
  for (let code = base; code <= peak; code++) {
    left += String.fromCharCode(code);
  }
  let right = "";
  for (let code = peak - 1; code >= base; code--) {
    right += String.fromCharCode(code);
  }
  console.log(" ".repeat(rows - 1 - r) + left + right);
}

    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

🔎 Worked Walkthrough — rows = 5

Trace each outer-loop value of r and see how leading spaces, peak letter, ascend, and descend produce each centered palindrome row.

Highlight rows: r = 0 (4 spaces, peak A, A only), r = 2 (2 spaces, peak C, ABCBA), r = 4 (0 spaces, peak E, ABCDEDCBA). Total letters printed: 1 + 3 + 5 + 7 + 9 = 25 = rows² for rows = 5.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices