Reverse Alphabet, Diagonal Star in JavaScript

What You’ll Learn

Print the reverse alphabet line EDCBA on every row, but replace one character per row with * where i === j. The star slides from right to left: EDCB*, EDC*A, ED*BA, E*CBA, *DCBA. Includes a live preview, worked JavaScript examples, edge cases, and complexity. Next: Program 18 (palindromic pyramid).

📝 Problem & Approach

Given a top letter (like E), print an n×n grid of reverse letters with one diagonal star per row.

# Classic sample (top = E)
# EDCB*
# EDC*A
# ED*BA
# E*CBA
# *DCBA

Inputs & Outputs

Minimal workflow

for i from base to top:
    line = ""
    for j from top down to base:
        line += (i === j ? "*" : String.fromCharCode(j))
    console.log(line)

Approach comparison

🔮 Live Preview

Enter a top letter from A to Z and draw the reverse diagonal-star grid in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs - fixed top E, user-chosen top letter, and a forward A..E diagonal variant. Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

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

for (let i = base; i <= top; i++) {
  let line = "";
  for (let j = top; j >= base; j--) {
    if (i === j) {
      line += "*";
    } else {
      line += String.fromCharCode(j);
    }
  }
  console.log(line);
}

EDCB*
EDC*A
ED*BA
E*CBA
*DCBA

const raw = (prompt("Enter the top letter (like E):") || "").trim().toUpperCase();
const top = raw ? raw.charCodeAt(0) : "E".charCodeAt(0);
const base = "A".charCodeAt(0);

for (let i = base; i <= top; i++) {
  let line = "";
  for (let j = top; j >= base; j--) {
    line += (i === j) ? "*" : String.fromCharCode(j);
  }
  console.log(line);
}

Enter the top letter (like E): D
DCB*
DC*A
D*BA
*CBA

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

for (let i = base; i <= top; i++) {
  let line = "";
  for (let j = base; j <= top; j++) {
    line += (i === j) ? "*" : String.fromCharCode(j);
  }
  console.log(line);
}

*BCDE
A*CDE
AB*DE
ABC*E
ABCD*

🔎 Worked Walkthrough — top E

Trace each outer value of i and see which column becomes the star.

Exactly one star per row; the match walks from right to left as i increases.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

With n = top − ‘A’ + 1, every row prints n characters, so total work is O(n²).

💡 Best Practices