algorithm-neet-code-top-150-python-visual/visual/0022_generate_parentheses.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>LC 22: Generate Parentheses - Algorithm Visualization</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">#22</span> Generate Parentheses</h1>
            <p>Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.</p>
            <div class="problem-meta">
                <span class="meta-tag">🔄 Backtracking</span>
                <span class="meta-tag">🔤 String</span>
                <span class="meta-tag">⏱️ O(4^n / √n)</span>
                <span class="meta-tag">💾 O(n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0022_generate_parentheses/0022_generate_parentheses.py</code>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>Backtracking builds strings by making choices at each step:</p>
            <ul>
                <li><strong>Two rules:</strong> (1) Can add '(' if we have pairs left, (2) Can add ')' only if there's an unmatched '('</li>
                <li><strong>Tree exploration:</strong> Each node makes choices, invalid paths are pruned automatically</li>
                <li><strong>Base case:</strong> When string length = 2n, we have a valid combination</li>
                <li><strong>Key insight:</strong> close_count < open_count ensures we never have more ')' than '('</li>
            </ul>
        </div>


        <div class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>

            <div class="controls">
                <label>n = </label>
                <select id="nValue" style="padding: 8px; border-radius: 5px; border: 2px solid #ddd;">
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3" selected>3</option>
                </select>
                <button class="btn btn-primary" onclick="step()">Step</button>
                <button class="btn btn-success" onclick="autoRun()">Auto Run</button>
                <button class="btn" style="background: #607d8b; color: white;" onclick="reset()">Reset</button>
            </div>

            <div class="status-message" id="statusMessage">
                Click Step to explore the backtracking tree
            </div>

            <div style="display: flex; gap: 30px; flex-wrap: wrap; margin-top: 20px;">
                <div style="flex: 2; min-width: 400px;">
                    <h4 style="margin-bottom: 10px;">🌳 Decision Tree</h4>
                    <svg id="treeViz" width="100%" height="400"></svg>
                </div>
                <div style="flex: 1; min-width: 200px;">
                    <h4 style="margin-bottom: 10px;">✅ Valid Combinations</h4>
                    <div id="resultsContainer" style="padding: 15px; background: #f5f5f5; border-radius: 12px; min-height: 200px;">
                        <span style="color: #999;">None yet...</span>
                    </div>

                    <h4 style="margin-top: 20px; margin-bottom: 10px;">📊 Current State</h4>
                    <div id="stateContainer" style="padding: 15px; background: #e3f2fd; border-radius: 12px;">
                        <div>Current: <strong id="currentStr">""</strong></div>
                        <div>Open: <strong id="openCount">0</strong></div>
                        <div>Close: <strong id="closeCount">0</strong></div>
                    </div>
                </div>
            </div>
        </div>
        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">generate_parenthesis</span>(n):
    results = []

    <span class="keyword">def</span> <span class="function">backtrack</span>(current, open_count, close_count):
        <span class="keyword">if</span> <span class="function">len</span>(current) == n * <span class="number">2</span>:
            results.<span class="function">append</span>(current)
            <span class="keyword">return</span>

        <span class="comment"># Can add '(' if we haven't used all</span>
        <span class="keyword">if</span> open_count < n:
            <span class="function">backtrack</span>(current + <span class="string">'('</span>, open_count + <span class="number">1</span>, close_count)

        <span class="comment"># Can add ')' only if we have unmatched '('</span>
        <span class="keyword">if</span> close_count < open_count:
            <span class="function">backtrack</span>(current + <span class="string">')'</span>, open_count, close_count + <span class="number">1</span>)

    <span class="function">backtrack</span>(<span class="string">''</span>, <span class="number">0</span>, <span class="number">0</span>)
    <span class="keyword">return</span> results</pre>
            </div>
        </div>
    </div>

    <script>
        let n = 3;
        let treeData = null;
        let nodeQueue = [];
        let results = [];
        let currentNode = null;
        let isRunning = false;
        let processedNodes = new Set();

        class TreeNode {
            constructor(str, open, close, parent = null, action = '') {
                this.str = str;
                this.open = open;
                this.close = close;
                this.parent = parent;
                this.action = action;
                this.children = [];
                this.id = `${str}_${open}_${close}`;
                this.visited = false;
                this.isValid = str.length === n * 2;
            }
        }

        function buildFullTree() {
            const root = new TreeNode('', 0, 0, null, 'start');
            buildTreeRecursive(root);
            return root;
        }

        function buildTreeRecursive(node) {
            if (node.str.length === n * 2) return;

            if (node.open < n) {
                const leftChild = new TreeNode(
                    node.str + '(',
                    node.open + 1,
                    node.close,
                    node,
                    'add ('
                );
                node.children.push(leftChild);
                buildTreeRecursive(leftChild);
            }

            if (node.close < node.open) {
                const rightChild = new TreeNode(
                    node.str + ')',
                    node.open,
                    node.close + 1,
                    node,
                    'add )'
                );
                node.children.push(rightChild);
                buildTreeRecursive(rightChild);
            }
        }

        function drawTree() {
            const svg = d3.select("#treeViz");
            svg.selectAll("*").remove();

            const container = svg.node().parentElement;
            const width = container.clientWidth;
            const height = 400;
            svg.attr("viewBox", `0 0 ${width} ${height}`);

            const g = svg.append("g").attr("transform", "translate(40, 30)");

            const treeLayout = d3.tree().size([width - 80, height - 80]);
            const hierarchy = d3.hierarchy(treeData);
            const treeNodes = treeLayout(hierarchy);

            // Draw links
            g.selectAll(".link")
                .data(treeNodes.links())
                .enter()
                .append("path")
                .attr("class", "link")
                .attr("d", d3.linkVertical()
                    .x(d => d.x)
                    .y(d => d.y))
                .attr("fill", "none")
                .attr("stroke", d => {
                    if (!d.target.data.visited) return "#e0e0e0";
                    return d.target.data.action === 'add (' ? "#667eea" : "#4caf50";
                })
                .attr("stroke-width", d => d.target.data.visited ? 3 : 1);

            // Draw nodes
            const nodes = g.selectAll(".node")
                .data(treeNodes.descendants())
                .enter()
                .append("g")
                .attr("class", "node")
                .attr("transform", d => `translate(${d.x}, ${d.y})`);

            nodes.append("circle")
                .attr("r", d => d.data.isValid ? 18 : 15)
                .attr("fill", d => {
                    if (d.data === currentNode) return "#ff9800";
                    if (d.data.isValid && d.data.visited) return "#4caf50";
                    if (d.data.visited) return "#667eea";
                    return "#e0e0e0";
                })
                .attr("stroke", d => d.data === currentNode ? "#f57c00" : "none")
                .attr("stroke-width", 3);

            nodes.append("text")
                .attr("dy", 4)
                .attr("text-anchor", "middle")
                .attr("font-size", d => d.data.isValid ? "10px" : "9px")
                .attr("fill", d => d.data.visited || d.data === currentNode ? "white" : "#666")
                .text(d => d.data.str || "ε");
        }

        function initQueue() {
            nodeQueue = [treeData];
        }

        function step() {
            if (nodeQueue.length === 0) {
                document.getElementById('statusMessage').textContent =
                    `Done! Found ${results.length} valid combinations`;
                return;
            }

            currentNode = nodeQueue.shift();
            currentNode.visited = true;

            document.getElementById('currentStr').textContent = `"${currentNode.str}"`;
            document.getElementById('openCount').textContent = currentNode.open;
            document.getElementById('closeCount').textContent = currentNode.close;

            if (currentNode.isValid) {
                results.push(currentNode.str);
                document.getElementById('statusMessage').textContent =
                    `Found valid combination: "${currentNode.str}"!`;
                renderResults();
            } else {
                let msg = `Exploring: "${currentNode.str}" (open: ${currentNode.open}, close: ${currentNode.close}). `;

                if (currentNode.open < n) {
                    msg += "Can add '('. ";
                    nodeQueue.push(currentNode.children.find(c => c.action === 'add ('));
                }
                if (currentNode.close < currentNode.open) {
                    msg += "Can add ')'. ";
                    nodeQueue.push(currentNode.children.find(c => c.action === 'add )'));
                }

                document.getElementById('statusMessage').textContent = msg;
            }

            // Filter out undefined entries
            nodeQueue = nodeQueue.filter(n => n !== undefined);
            drawTree();
        }

        function autoRun() {
            if (isRunning) return;
            isRunning = true;

            const interval = setInterval(() => {
                if (nodeQueue.length === 0) {
                    clearInterval(interval);
                    isRunning = false;
                    document.getElementById('statusMessage').textContent =
                        `Complete! Found ${results.length} valid combinations: [${results.map(r => `"${r}"`).join(', ')}]`;
                    return;
                }
                step();
            }, 500);
        }

        function renderResults() {
            const container = document.getElementById('resultsContainer');
            if (results.length === 0) {
                container.innerHTML = '<span style="color: #999;">None yet...</span>';
                return;
            }
            container.innerHTML = results.map((r, i) => `
                <div style="padding: 8px 12px; margin: 5px 0; background: #e8f5e9;
                            border-radius: 6px; font-family: monospace; font-weight: bold;
                            color: #2e7d32;">
                    ${i + 1}. ${r}

        </div>
            `).join('');
        }

        function reset() {
            n = parseInt(document.getElementById('nValue').value);
            treeData = buildFullTree();
            results = [];
            currentNode = null;
            isRunning = false;
            initQueue();

            document.getElementById('statusMessage').textContent =
                `Click Step to explore backtracking with n=${n}`;
            document.getElementById('currentStr').textContent = '""';
            document.getElementById('openCount').textContent = '0';
            document.getElementById('closeCount').textContent = '0';

            renderResults();
            drawTree();
        }

        document.getElementById('nValue').addEventListener('change', reset);
        reset();
        window.addEventListener('resize', drawTree);
    </script>
</body>
</html>