algorithm-neet-code-top-150-python-visual/visual/0014_longest_common_prefix.html at main · kimtth/algorithm-neet-code-top-150-python-visual · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Longest Common Prefix - LeetCode 14</title>
    <link rel="stylesheet" href="styles.css">
    <script src="https://d3js.org/d3.v7.min.js"></script>
</head>
<body>
    <div class="container">
        <div class="problem-info">
            <h1><span class="problem-number">#14</span> Longest Common Prefix</h1>
            <p>Find the longest common prefix string amongst an array of strings.</p>
            <div class="problem-meta">
                <span class="meta-tag">String</span>
                <span class="meta-tag">Easy</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0014_longest_common_prefix/0014_longest_common_prefix.py</code>
            </div>

        </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>Dynamic Programming <strong>breaks big problems into smaller ones</strong>:</p>
            <ul>
                <li><strong>Subproblems:</strong> Solve smaller versions first</li>
                <li><strong>Memoization:</strong> Cache results to avoid recalculation</li>
                <li><strong>Build up:</strong> Combine small solutions for final answer</li>
                <li><strong>State:</strong> Define what each position represents</li>
            </ul>
        </div>


        <div class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>
            <div class="controls">
                <button id="stepBtn">Step</button>
                <button id="autoBtn">Auto Run</button>
                <button id="resetBtn">Reset</button>
            </div>
            <svg id="mainSvg" width="800" height="350"></svg>
            <div class="status-message" id="status">Click "Step" to find longest common prefix</div>
        </div>

        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">longestCommonPrefix</span>(strs: <span class="class-name">List</span>[str]) -> str:
    <span class="keyword">if</span> <span class="keyword">not</span> strs:
        <span class="keyword">return</span> <span class="string">""</span>

    <span class="comment"># Vertical scanning</span>
    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(strs[<span class="number">0</span>])):
        char = strs[<span class="number">0</span>][i]
        <span class="keyword">for</span> j <span class="keyword">in</span> <span class="function">range</span>(<span class="number">1</span>, <span class="function">len</span>(strs)):
            <span class="keyword">if</span> i >= <span class="function">len</span>(strs[j]) <span class="keyword">or</span> strs[j][i] != char:
                <span class="keyword">return</span> strs[<span class="number">0</span>][:<span class="class-name">i</span>]

    <span class="keyword">return</span> strs[<span class="number">0</span>]</pre>
            </div>
        </div>
    </div>

    <script>
        const strs = ["flower", "flow", "flight"];
        const width = 800, height = 350;
        const svg = d3.select("#mainSvg");

        let charIndex = 0;
        let strIndex = 0;
        let prefix = "";
        let phase = 'comparing';
        let mismatch = false;

        let autoTimer = null;
        let autoRunning = false;

        function draw() {
            svg.selectAll("*").remove();

            const cellWidth = 45, cellHeight = 50;
            const startX = 120, startY = 70;

            // Title
            svg.append("text")
                .attr("x", width / 2).attr("y", 30)
                .attr("text-anchor", "middle")
                .attr("font-weight", "bold")
                .text(`Finding Longest Common Prefix in [${strs.map(s => `"${s}"`).join(", ")}]`);

            // Draw strings
            strs.forEach((str, sIdx) => {
                svg.append("text")
                    .attr("x", 30).attr("y", startY + sIdx * cellHeight + 30)
                    .attr("font-size", "14px")
                    .attr("fill", "#666")
                    .text(`strs[${sIdx}]:`);

                for (let cIdx = 0; cIdx < str.length; cIdx++) {
                    const x = startX + cIdx * cellWidth;
                    const y = startY + sIdx * cellHeight;

                    let fill = "#f8fafc", stroke = "#94a3b8";

                    if (cIdx < charIndex) {
                        fill = "#d1fae5"; stroke = "#10b981";
                    } else if (cIdx === charIndex) {
                        if (sIdx === strIndex) {
                            fill = "#fef3c7"; stroke = "#f59e0b";
                        } else if (sIdx < strIndex) {
                            fill = "#d1fae5"; stroke = "#10b981";
                        }
                        if (mismatch && sIdx === strIndex) {
                            fill = "#fee2e2"; stroke = "#ef4444";
                        }
                    }

                    svg.append("rect")
                        .attr("x", x).attr("y", y)
                        .attr("width", cellWidth - 5).attr("height", cellHeight - 5)
                        .attr("rx", 6)
                        .attr("fill", fill).attr("stroke", stroke)
                        .attr("stroke-width", cIdx === charIndex && sIdx === strIndex ? 3 : 2);

                    svg.append("text")
                        .attr("x", x + (cellWidth - 5) / 2)
                        .attr("y", y + (cellHeight - 5) / 2 + 6)
                        .attr("text-anchor", "middle")
                        .attr("font-size", "20px")
                        .attr("font-weight", "bold")
                        .text(str[cIdx]);
                }
            });

            // Column indicator
            if (charIndex < strs[0].length && !mismatch) {
                svg.append("text")
                    .attr("x", startX + charIndex * cellWidth + (cellWidth - 5) / 2)
                    .attr("y", startY - 15)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "12px")
                    .attr("fill", "#f59e0b")
                    .text(`▼ Column ${charIndex}`);
            }

            // Current prefix
            const prefixY = startY + strs.length * cellHeight + 30;

            svg.append("rect")
                .attr("x", 120).attr("y", prefixY)
                .attr("width", 300).attr("height", 50)
                .attr("rx", 10)
                .attr("fill", "#e8f5e9").attr("stroke", "#4caf50");

            svg.append("text")
                .attr("x", 270).attr("y", prefixY + 20)
                .attr("text-anchor", "middle")
                .attr("font-size", "12px")
                .text("Current Prefix:");

            svg.append("text")
                .attr("x", 270).attr("y", prefixY + 40)
                .attr("text-anchor", "middle")
                .attr("font-size", "20px")
                .attr("font-weight", "bold")
                .attr("fill", "#2e7d32")
                .text(prefix ? `"${prefix}"` : '""');

            // Final result
            if (phase === 'done') {
                svg.append("rect")
                    .attr("x", 450).attr("y", prefixY)
                    .attr("width", 250).attr("height", 50)
                    .attr("rx", 10)
                    .attr("fill", "#d1fae5").attr("stroke", "#10b981")
                    .attr("stroke-width", 2);

                svg.append("text")
                    .attr("x", 575).attr("y", prefixY + 32)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "18px")
                    .attr("font-weight", "bold")
                    .attr("fill", "#10b981")
                    .text(`Result: "${prefix}"`);
            }

            // Legend
            const legendY = 290;
            const legend = [
                { color: "#d1fae5", label: "Matched" },
                { color: "#fef3c7", label: "Comparing" },
                { color: "#fee2e2", label: "Mismatch" }
            ];

            legend.forEach((item, i) => {
                svg.append("rect")
                    .attr("x", 500 + i * 100).attr("y", legendY)
                    .attr("width", 15).attr("height", 15)
                    .attr("fill", item.color)
                    .attr("stroke", "#999");

                svg.append("text")
                    .attr("x", 520 + i * 100).attr("y", legendY + 12)
                    .attr("font-size", "11px")
                    .text(item.label);
            });
        }

        function step() {
            if (phase === 'done') return false;

            // Check if we've gone through all characters
            if (charIndex >= strs[0].length) {
                phase = 'done';
                document.getElementById("status").textContent =
                    `Done! Longest common prefix: "${prefix}"`;
                draw();
                return false;
            }

            const targetChar = strs[0][charIndex];

            if (strIndex === 0) {
                document.getElementById("status").textContent =
                    `Checking column ${charIndex}: comparing '${targetChar}'`;
                strIndex = 1;
            } else {
                // Check if current string has this character
                if (charIndex >= strs[strIndex].length || strs[strIndex][charIndex] !== targetChar) {
                    mismatch = true;
                    phase = 'done';
                    document.getElementById("status").textContent =
                        charIndex >= strs[strIndex].length
                            ? `String "${strs[strIndex]}" is too short. Done!`
                            : `Mismatch: '${strs[strIndex][charIndex]}' ≠ '${targetChar}'. Done!`;
                    draw();
                    return false;
                }

                document.getElementById("status").textContent =
                    `'${strs[strIndex][charIndex]}' matches '${targetChar}'`;

                strIndex++;

                // All strings matched at this position
                if (strIndex >= strs.length) {
                    prefix += targetChar;
                    charIndex++;
                    strIndex = 0;
                    document.getElementById("status").textContent =
                        `All matched! Prefix is now "${prefix}"`;
                }
            }

            draw();
            return phase !== 'done';
        }

        function reset() {
            charIndex = 0;
            strIndex = 0;
            prefix = "";
            phase = 'comparing';
            mismatch = false;
            if (autoTimer) clearInterval(autoTimer);
            autoRunning = false;
            document.getElementById("autoBtn").textContent = "Auto Run";
            document.getElementById("status").textContent = 'Click "Step" to find longest common prefix';
            draw();
        }

        function autoRun() {
            if (autoRunning) {
                clearInterval(autoTimer);
                autoRunning = false;
                document.getElementById("autoBtn").textContent = "Auto Run";
            } else {
                autoRunning = true;
                document.getElementById("autoBtn").textContent = "Pause";
                autoTimer = setInterval(() => {
                    if (!step()) {
                        clearInterval(autoTimer);
                        autoRunning = false;
                        document.getElementById("autoBtn").textContent = "Auto Run";
                    }
                }, 600);
            }
        }

        document.getElementById("stepBtn").addEventListener("click", step);
        document.getElementById("autoBtn").addEventListener("click", autoRun);
        document.getElementById("resetBtn").addEventListener("click", reset);

        reset();
    </script>
</body>
</html>