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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>Q42: Maximum Depth of Binary Tree - BFS</title>
    <link rel="stylesheet" href="visual.css">
    <script src="https://d3js.org/d3.v7.min.js"></script>

</head>
<body>
    <div class="container">
        <div class="problem-info">
            <h1>Q42: Maximum Depth of Binary Tree</h1>
            <p>Find the maximum depth (height) of a binary tree using BFS level-by-level traversal.</p>
            <div class="problem-meta">
                <span class="meta-tag">📁 Tree</span>
                <span class="meta-tag">⏱️ O(n)</span>
                <span class="meta-tag">💡 BFS Level Order</span>
            </div>
        </div>


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

            <div class="controls">
                <button class="btn btn-primary" id="stepBtn" onclick="step()">Step</button>
                <button class="btn btn-success" id="autoBtn" onclick="toggleAuto()">Auto Run</button>
                <button class="btn btn-warning" onclick="reset()">Reset</button>
            </div>

            <div class="legend">
                <div class="legend-item"><div class="legend-circle bg-cyan"></div> Unvisited</div>
                <div class="legend-item"><div class="legend-circle bg-orange-deep"></div> Current Level</div>
                <div class="legend-item"><div class="legend-circle bg-lime"></div> Visited</div>
            </div>

            <div class="status-message" id="statusMessage">
                Tree: [3, 9, 20, 4, 6, 15, 7]. Click Step to start BFS traversal.
            </div>

            <div class="info-section">
                <div class="info-box highlight">
                    <div class="info-label">Current Depth</div>
                    <div class="info-value" id="depthValue">0</div>
                </div>
            </div>

            <div class="tree-container">
                <svg id="tree" width="600" height="300"></svg>
            </div>

            <div class="queue-section">
                <div class="queue-title">📚 Queue (nodes at current level)</div>
                <div class="queue-items" id="queueDisplay"><span class="text-gray">Empty</span></div>
            </div>
        </div>
    </div>

        <div class="code-section">
            <h3>📄 Python Solution (42-1.py)</h3>
            <pre><span class="keyword">import</span> collections


<span class="comment"># Definition for a binary tree node.</span>
<span class="keyword">class</span> TreeNode:
    <span class="keyword">def</span> <span class="function">__init__</span>(<span class="keyword">self</span>, x):
        <span class="keyword">self</span>.val = x
        <span class="keyword">self</span>.left = <span class="keyword">None</span>
        <span class="keyword">self</span>.right = <span class="keyword">None</span>


<span class="keyword">class</span> Solution:
    <span class="keyword">def</span> <span class="function">maxDepth</span>(<span class="keyword">self</span>, root: TreeNode) -&gt; int:
        <span class="keyword">if</span> root is <span class="keyword">None</span>:
            <span class="keyword">return</span> <span class="number">0</span>
        queue = collections.<span class="function">deque</span>([root])
        depth = <span class="number">0</span>

        <span class="keyword">while</span> queue:
            depth += <span class="number">1</span>
            <span class="comment"># 큐 연산 추출 노드의 자식 노드 삽입</span>
            <span class="keyword">for</span> _ <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(queue)):
                cur_root = queue.<span class="function">popleft</span>()
                <span class="keyword">if</span> cur_root.left:
                    queue.<span class="function">append</span>(cur_root.left)
                <span class="keyword">if</span> cur_root.right:
                    queue.<span class="function">append</span>(cur_root.right)
        <span class="comment"># BFS 반복 횟수 == 깊이</span>
        <span class="keyword">return</span> depth</pre>
        </div>

    </div>

    <script>
        const treeData = {
            val: 3,
            left: { val: 9, left: { val: 4 }, right: { val: 6 } },
            right: { val: 20, left: { val: 15 }, right: { val: 7 } }
        };

        let nodes = [];
        let links = [];
        let queue = [];
        let depth = 0;
        let currentLevel = [];
        let visited = new Set();
        let done = false;
        let autoInterval = null;

        function buildTree(node, x, y, dx, depth = 0, parent = null) {
            if (!node) return;
            const nodeData = { val: node.val, x, y, depth, id: nodes.length };
            nodes.push(nodeData);
            if (parent !== null) {
                links.push({ source: parent, target: nodeData });
            }
            if (node.left) buildTree(node.left, x - dx, y + 70, dx / 2, depth + 1, nodeData);
            if (node.right) buildTree(node.right, x + dx, y + 70, dx / 2, depth + 1, nodeData);
        }

        function init() {
            nodes = [];
            links = [];
            queue = [];
            currentLevel = [];
            visited = new Set();
            depth = 0;
            done = false;

            buildTree(treeData, 300, 50, 120);
            queue = [nodes[0]];
            renderTree();
            renderQueue();
        }

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

            // Draw links
            links.forEach(link => {
                svg.append("line")
                    .attr("x1", link.source.x)
                    .attr("y1", link.source.y)
                    .attr("x2", link.target.x)
                    .attr("y2", link.target.y)
                    .attr("stroke", "#999")
                    .attr("stroke-width", 2);
            });

            // Draw nodes
            nodes.forEach(node => {
                let fill = "#3498db";
                if (visited.has(node.id)) fill = "#27ae60";
                if (currentLevel.includes(node.id)) fill = "#f39c12";

                svg.append("circle")
                    .attr("cx", node.x)
                    .attr("cy", node.y)
                    .attr("r", 25)
                    .attr("fill", fill)
                    .attr("stroke", "#333")
                    .attr("stroke-width", 2);

                svg.append("text")
                    .attr("x", node.x)
                    .attr("y", node.y + 5)
                    .attr("text-anchor", "middle")
                    .attr("fill", "white")
                    .attr("font-weight", "bold")
                    .attr("font-size", "14px")
                    .text(node.val);
            });
        }

        function renderQueue() {
            const container = document.getElementById('queueDisplay');
            if (queue.length === 0) {
                container.innerHTML = '<span class="text-gray">Empty</span>';
            } else {
                container.innerHTML = queue.map(n =>
                    `<div class="queue-item">${n.val}</div>`
                ).join('');
            }
        }

        function step() {
            if (done) {
                document.getElementById('stepBtn').disabled = true;
                stopAuto();
                return;
            }

            if (queue.length === 0) {
                done = true;
                currentLevel = [];
                document.getElementById('statusMessage').textContent =
                    `✅ BFS Complete! Maximum Depth = ${depth}`;
                document.getElementById('stepBtn').disabled = true;
                stopAuto();
                renderTree();
                return;
            }

            // Process entire level
            depth++;
            document.getElementById('depthValue').textContent = depth;

            const levelSize = queue.length;
            currentLevel = queue.map(n => n.id);
            const levelVals = queue.map(n => n.val);

            // Mark all as visited and collect children
            const nextQueue = [];
            queue.forEach(node => {
                visited.add(node.id);
                // Find children
                links.forEach(link => {
                    if (link.source.id === node.id) {
                        nextQueue.push(link.target);
                    }
                });
            });

            queue = nextQueue;

            document.getElementById('statusMessage').textContent =
                `Level ${depth}: Processed nodes [${levelVals.join(', ')}]. Added ${nextQueue.length} children.`;

            renderTree();
            renderQueue();
        }

        function toggleAuto() {
            if (autoInterval) { stopAuto(); }
            else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(step, 1000);
            }
        }

        function stopAuto() {
            if (autoInterval) { clearInterval(autoInterval); autoInterval = null; }
            document.getElementById('autoBtn').textContent = 'Auto Run';
        }

        function reset() {
            stopAuto();
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').textContent =
                'Tree: [3, 9, 20, 4, 6, 15, 7]. Click Step to start BFS traversal.';
            document.getElementById('depthValue').textContent = '0';
            init();
        }

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