Palindrome Checker

This is a standalone SketchWave example that visually demonstrates how a recursive isPalindrome() function works, using animated SWCharacter objects to bring each step of the recursion to life on a live canvas.

💡 How This Example Works

Type a word or phrase — or use the preloaded classic "Never odd or even!" — and press 🔍 Analyze. The app strips spaces and punctuation with a pop animation, slides the remaining letters to their new centered positions, then begins the animated palindrome analysis.

• Each letter is drawn as a colored SWCharacter on the grid.
• Spaces and punctuation are removed with a pop-and-shrink animation before analysis starts.
• The algorithm works from the outside in, flying each outer pair upward to compare them.
• Matched pairs scatter off screen; mismatches shake and dim the whole word.
• A successful palindrome triggers a celebration wave.
• Press G to toggle the grid on or off at any time.
• 🔍 Analyze / ⏸ Pause — runs or pauses the animation.
• ↺ Reset — clears the animation and restores all letters.
• 💾 Save Image — captures a snapshot of the canvas.
• Use the Letter size, Letter spacing, and Animation speed sliders to customize the display.

🧑‍💻 Developer Notes

Developer

klp

Date

March 28, 2026

Commentary

Stage 1: word input with preloaded phrase "Never odd or even!", animated isPalindrome() visualization with strip/slide preprocessing, pair-comparison state machine, and adjustable size, spacing, and speed controls.

📄 isPalindrome() Source Code

The animation visualizes the following recursive function. Each comparison of the outer pair corresponds to one FLY_UP → TAP → FLY_AWAY animation cycle.

/**
 * Returns true if str is a palindrome (reads the same
 * forwards and backwards), ignoring case.
 *
 * Preprocessing: strip all non-alphanumeric characters
 * and convert to lowercase before calling.
 *
 * @param  {string} str  - cleaned, lowercase input string
 * @returns {boolean}
 */
function isPalindrome(str) {
    // Base cases — empty string or single character
    if (str.length <= 1) return true;

    // Mismatch on the outer pair → not a palindrome
    if (str[0] !== str[str.length - 1]) return false;

    // Recurse on the inner substring (strip one char from each end)
    return isPalindrome(str.slice(1, str.length - 1));
}

/**
 * Returns true if s is a palindrome (reads the same
 * forwards and backwards), ignoring case.
 *
 * Preprocessing: strip all non-alphanumeric characters
 * and convert to lowercase before calling.
 *
 * @param  s  cleaned, lowercase input string
 * @return    true if s is a palindrome
 */
public static boolean isPalindrome(String s) {
    // Base cases — empty string or single character
    if (s.length() <= 1) return true;

    // Mismatch on the outer pair → not a palindrome
    if (s.charAt(0) != s.charAt(s.length() - 1)) return false;

    // Recurse on the inner substring (strip one char from each end)
    return isPalindrome(s.substring(1, s.length() - 1));
}

def is_palindrome(s: str) -> bool:
    """
    Returns True if s is a palindrome (reads the same
    forwards and backwards), ignoring case.

    Preprocessing: strip all non-alphanumeric characters
    and convert to lowercase before calling.

    Args:
        s: cleaned, lowercase input string
    Returns:
        True if s is a palindrome
    """
    # Base cases — empty string or single character
    if len(s) <= 1:
        return True

    # Mismatch on the outer pair → not a palindrome
    if s[0] != s[-1]:
        return False

    # Recurse on the inner substring (strip one char from each end)
    return is_palindrome(s[1:-1])