algorithm-neet-code-top-150-python-visual/visual/0226_invert_binary_tree.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 226: Invert Binary Tree - 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">#226</span> Invert Binary Tree</h1>
            <p>Given the root of a binary tree, invert the tree (swap left and right children at every node), and return its root.</p>
            <div class="problem-meta">
                <span class="meta-tag">🌳 Binary Tree</span>
                <span class="meta-tag">🔄 Recursion</span>
                <span class="meta-tag">⏱️ O(n)</span>
                <span class="meta-tag">💾 O(h) stack</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0226_invert_binary_tree/0226_invert_binary_tree.py</code>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>Think of it like looking at a tree in a mirror:</p>
            <ul>
                <li><strong>At each node:</strong> Swap the left and right children</li>
                <li><strong>Recursively:</strong> Do this for every node in the tree</li>
                <li><strong>Order:</strong> We go deep first (post-order), then swap on the way back up</li>
                <li><strong>Result:</strong> The entire tree is mirrored!</li>
            </ul>
        </div>


        <div class="visualization-section">
            <h3>🎬 Step-by-Step 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="info-box secondary" style="margin-bottom: 20px;">
                🌳 Input Tree: <strong>[4, 2, 7, 1, 3, 6, 9]</strong>
            </div>

            <div class="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to start visualization
            </div>

            <div style="display: flex; gap: 40px; justify-content: center; flex-wrap: wrap;">
                <div>
                    <h4 style="text-align: center; margin-bottom: 10px;">Original Tree</h4>
                    <div id="originalTreeContainer" style="width: 350px; height: 300px; background: #f5f5f5; border-radius: 12px;"></div>
                </div>
                <div>
                    <h4 style="text-align: center; margin-bottom: 10px;">Current State</h4>
                    <div id="currentTreeContainer" style="width: 350px; height: 300px; background: #e8f5e9; border-radius: 12px;"></div>
                </div>
            </div>

            <div class="explanation-panel" style="margin-top: 20px;">
                <h4>📝 Recursion Stack</h4>
                <div id="stackDisplay" style="display: flex; gap: 10px; flex-wrap: wrap; padding: 10px;">
                    <span style="color: #666;">Empty - Click Step to begin</span>
                </div>
            </div>
        </div>
        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">invert_tree</span>(self, root: <span class="class-name">TreeNode</span>) -> TreeNode:
    <span class="keyword">if</span> root <span class="keyword">is</span> <span class="keyword">None</span>:
        <span class="keyword">return</span> <span class="keyword">None</span>

    <span class="comment"># Recursively invert subtrees</span>
    right = self.<span class="function">invert_tree</span>(root.right)
    left = self.<span class="function">invert_tree</span>(root.left)

    <span class="comment"># Swap children</span>
    root.left = right
    root.right = left

    <span class="keyword">return</span> root</pre>
            </div>
        </div>
    </div>

    <script>
        // Tree structure: [4, 2, 7, 1, 3, 6, 9]
        //        4
        //       / \
        //      2   7
        //     / \ / \
        //    1  3 6  9

        const originalTree = {
            val: 4,
            left: {
                val: 2,
                left: { val: 1, left: null, right: null },
                right: { val: 3, left: null, right: null }
            },
            right: {
                val: 7,
                left: { val: 6, left: null, right: null },
                right: { val: 9, left: null, right: null }
            }
        };

        let currentTree;
        let steps = [];
        let currentStepIdx = -1;
        let autoInterval = null;

        function deepCopy(obj) {
            return JSON.parse(JSON.stringify(obj));
        }

        function generateSteps(node, path = []) {
            if (node === null) return;

            steps.push({
                type: 'visit',
                path: [...path],
                val: node.val,
                message: `Visiting node ${node.val}`
            });

            // Visit children first (post-order)
            if (node.left) generateSteps(node.left, [...path, 'left']);
            if (node.right) generateSteps(node.right, [...path, 'right']);

            // Then swap
            if (node.left || node.right) {
                steps.push({
                    type: 'swap',
                    path: [...path],
                    val: node.val,
                    leftVal: node.left?.val || 'null',
                    rightVal: node.right?.val || 'null',
                    message: `Swapping children of node ${node.val}: ${node.left?.val || 'null'} ↔ ${node.right?.val || 'null'}`
                });
            }
        }

        function getNode(tree, path) {
            let node = tree;
            for (const dir of path) {
                node = node[dir];
            }
            return node;
        }

        function swapChildren(tree, path) {
            const node = getNode(tree, path);
            const temp = node.left;
            node.left = node.right;
            node.right = temp;
        }

        function init() {
            currentTree = deepCopy(originalTree);
            steps = [];
            generateSteps(originalTree);
            renderTree('originalTreeContainer', originalTree, null, false);
            renderTree('currentTreeContainer', currentTree, null, false);
        }

        function renderTree(containerId, tree, highlightPath, showSwap) {
            const container = document.getElementById(containerId);
            const width = container.offsetWidth;
            const height = container.offsetHeight;

            d3.select(`#${containerId}`).selectAll('*').remove();

            const svg = d3.select(`#${containerId}`)
                .append('svg')
                .attr('width', width)
                .attr('height', height);

            const nodeRadius = 25;
            const levelHeight = 70;

            function getPositions(node, x, y, level, dx) {
                if (!node) return [];

                const positions = [{ node, x, y, level }];
                const childDx = dx / 2;

                if (node.left) {
                    positions.push(...getPositions(node.left, x - dx, y + levelHeight, level + 1, childDx));
                }
                if (node.right) {
                    positions.push(...getPositions(node.right, x + dx, y + levelHeight, level + 1, childDx));
                }

                return positions;
            }

            const positions = getPositions(tree, width / 2, 40, 0, 80);
            const posMap = new Map();
            positions.forEach(p => posMap.set(p.node, p));

            // Draw edges
            positions.forEach(({ node, x, y }) => {
                if (node.left) {
                    const childPos = posMap.get(node.left);
                    svg.append('line')
                        .attr('x1', x)
                        .attr('y1', y + nodeRadius)
                        .attr('x2', childPos.x)
                        .attr('y2', childPos.y - nodeRadius)
                        .attr('stroke', '#999')
                        .attr('stroke-width', 2);
                }
                if (node.right) {
                    const childPos = posMap.get(node.right);
                    svg.append('line')
                        .attr('x1', x)
                        .attr('y1', y + nodeRadius)
                        .attr('x2', childPos.x)
                        .attr('y2', childPos.y - nodeRadius)
                        .attr('stroke', '#999')
                        .attr('stroke-width', 2);
                }
            });

            // Draw nodes
            positions.forEach(({ node, x, y }) => {
                const g = svg.append('g')
                    .attr('transform', `translate(${x}, ${y})`);

                let fillColor = '#fff';
                let strokeColor = '#667eea';

                // Check if this node is highlighted
                if (highlightPath !== null) {
                    let testNode = tree;
                    let isMatch = true;
                    for (const dir of highlightPath) {
                        testNode = testNode[dir];
                    }
                    if (testNode === node) {
                        fillColor = showSwap ? '#ff9800' : '#4caf50';
                        strokeColor = showSwap ? '#e65100' : '#2e7d32';
                    }
                }

                g.append('circle')
                    .attr('r', nodeRadius)
                    .attr('fill', fillColor)
                    .attr('stroke', strokeColor)
                    .attr('stroke-width', 3);

                g.append('text')
                    .attr('text-anchor', 'middle')
                    .attr('dy', 5)
                    .attr('font-size', '16px')
                    .attr('font-weight', 'bold')
                    .attr('fill', fillColor === '#fff' ? '#333' : '#fff')
                    .text(node.val);
            });
        }

        function updateStackDisplay() {
            const container = document.getElementById('stackDisplay');

            if (currentStepIdx < 0) {
                container.innerHTML = '<span style="color: #666;">Empty - Click Step to begin</span>';
                return;
            }

            // Build stack from steps up to current
            const stack = [];
            for (let i = 0; i <= currentStepIdx; i++) {
                const step = steps[i];
                if (step.type === 'visit') {
                    stack.push(step.val);
                } else if (step.type === 'swap') {
                    // Pop after swap (returning from recursion)
                    const idx = stack.lastIndexOf(step.val);
                    if (idx !== -1) stack.splice(idx, 1);
                }
            }

            if (stack.length === 0) {
                container.innerHTML = '<span style="color: #4caf50;">✅ Recursion complete!</span>';
                return;
            }

            container.innerHTML = stack.map((val, i) =>
                `<div style="padding: 5px 15px; background: ${i === stack.length - 1 ? '#667eea' : '#e0e0e0'};
                color: ${i === stack.length - 1 ? 'white' : '#333'}; border-radius: 5px; font-weight: bold;">
                    ${val}

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

        function step() {
            currentStepIdx++;

            if (currentStepIdx >= steps.length) {
                document.getElementById('statusMessage').className = 'status-message success';
                document.getElementById('statusMessage').textContent = '✅ Tree inversion complete!';
                document.getElementById('stepBtn').disabled = true;
                stopAuto();
                return;
            }

            const stepData = steps[currentStepIdx];
            document.getElementById('statusMessage').textContent = stepData.message;

            if (stepData.type === 'swap') {
                swapChildren(currentTree, stepData.path);
                renderTree('currentTreeContainer', currentTree, stepData.path, true);
            } else {
                renderTree('currentTreeContainer', currentTree, stepData.path, false);
            }

            updateStackDisplay();
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (currentStepIdx >= steps.length - 1) {
                        step();
                        stopAuto();
                    } else {
                        step();
                    }
                }, 800);
            }
        }

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

        function reset() {
            stopAuto();
            currentStepIdx = -1;
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').className = 'status-message';
            document.getElementById('statusMessage').textContent = 'Click "Step" or "Auto Run" to start visualization';
            init();
        }

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