algorithm-neet-code-top-150-python-visual/visual/0239_sliding_window_maximum.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>Sliding Window Maximum - LeetCode 239</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">#239</span> Sliding Window Maximum</h1>
            <p>Given an array and a window size k, slide a window across the array and return the maximum value in each window position. Uses a monotonic deque for O(n) efficiency!</p>
            <div class="problem-meta">
                <span class="meta-tag">🪟 Sliding Window</span>
                <span class="meta-tag">📚 Monotonic Deque</span>
                <span class="meta-tag">⏱️ O(n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <a href="../python/0239_sliding_window_maximum/0239_sliding_window_maximum.py">0239_sliding_window_maximum.py</a>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>💡 How It Works (Layman's Terms)</h4>
            <ul>
                <li><strong>Problem:</strong> Find the maximum in every window of size k as it slides across</li>
                <li><strong>Naive approach:</strong> Check all k elements for each window → O(n×k)</li>
                <li><strong>Smart approach:</strong> Use a "monotonic deque" → O(n)</li>
                <li><strong>Monotonic Deque:</strong> Keeps elements in decreasing order. Front is always the max!</li>
                <li><strong>Key insight:</strong> If a new element is bigger than previous ones, those smaller ones can never be the max (they'll leave the window before the new element)</li>
                <li><strong>Remove from back:</strong> Pop smaller elements from deque back</li>
                <li><strong>Remove from front:</strong> Pop elements outside the current window</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">
                Window Size (k) = 3
            </div>

            <div class="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to see how the monotonic deque finds maximums
            </div>

            <div class="array-section">
                <div class="array-label">Array (nums):</div>
                <div class="array-container" id="arrayContainer"></div>
            </div>

            <div class="array-section">
                <div class="array-label">Deque (stores indices, front = max):</div>
                <div class="queue-container" id="dequeContainer" style="min-height: 60px;"></div>
            </div>

            <div class="array-section">
                <div class="array-label">Result (maximums):</div>
                <div class="array-container" id="resultContainer"></div>
            </div>
        </div>

        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">maxSlidingWindow</span>(self, nums: List[<span class="class-name">int</span>], k: <span class="class-name">int</span>) -> List[<span class="class-name">int</span>]:
    result = []
    dq = deque()  <span class="comment"># stores indices, front is always max</span>

    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(nums)):
        <span class="comment"># Remove indices outside window</span>
        <span class="keyword">while</span> dq <span class="keyword">and</span> dq[<span class="number">0</span>] < i - k + <span class="number">1</span>:
            dq.popleft()

        <span class="comment"># Remove smaller elements (they're useless)</span>
        <span class="keyword">while</span> dq <span class="keyword">and</span> nums[dq[-<span class="number">1</span>]] < nums[i]:
            dq.pop()

        dq.append(i)

        <span class="comment"># Window is full, record max</span>
        <span class="keyword">if</span> i >= k - <span class="number">1</span>:
            result.append(nums[dq[<span class="number">0</span>]])

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

    <script>
        const nums = [1, 3, -1, -3, 5, 3, 6, 7];
        const k = 3;
        let deque = []; // stores indices
        let result = [];
        let currentIndex = 0;
        let phase = 'init';
        let autoInterval = null;

        function init() {
            renderArray();
            renderDeque();
            renderResult();
        }

        function renderArray() {
            const container = document.getElementById('arrayContainer');
            container.innerHTML = '';
            nums.forEach((num, idx) => {
                const box = document.createElement('div');
                box.className = 'array-box';
                box.id = `num-${idx}`;
                box.innerHTML = `${num}<span class="index-label">[${idx}]</span>`;
                // Highlight current window
                if (phase !== 'init' && idx >= Math.max(0, currentIndex - k + 1) && idx <= currentIndex) {
                    box.classList.add('current');
                }
                if (idx === currentIndex && phase !== 'init' && phase !== 'done') {
                    box.classList.add('highlight');
                }
                container.appendChild(box);
            });
        }

        function renderDeque() {
            const container = document.getElementById('dequeContainer');
            container.innerHTML = '';
            if (deque.length === 0) {
                container.innerHTML = '<span style="color: #999; padding: 10px;">Empty</span>';
                return;
            }
            deque.forEach((idx, pos) => {
                const item = document.createElement('div');
                item.className = 'queue-item';
                if (pos === 0) {
                    item.style.background = 'linear-gradient(135deg, #4caf50 0%, #8bc34a 100%)';
                }
                item.innerHTML = `${nums[idx]}<br><small>[${idx}]</small>`;
                container.appendChild(item);
            });
        }

        function renderResult() {
            const container = document.getElementById('resultContainer');
            container.innerHTML = '';
            result.forEach((val, idx) => {
                const box = document.createElement('div');
                box.className = 'array-box complete';
                box.innerHTML = `${val}<span class="index-label">[${idx}]</span>`;
                container.appendChild(box);
            });
            if (result.length === 0) {
                container.innerHTML = '<span style="color: #999;">Results will appear here...</span>';
            }
        }

        function step() {
            if (phase === 'init') {
                phase = 'processing';
                currentIndex = 0;
                document.getElementById('statusMessage').textContent = 'Starting to process array with monotonic deque...';
            }

            if (phase === 'processing') {
                if (currentIndex >= nums.length) {
                    phase = 'done';
                    document.getElementById('statusMessage').textContent =
                        `✅ Done! Maximum in each window: [${result.join(', ')}]`;
                    document.getElementById('stepBtn').disabled = true;
                    stopAuto();
                    renderArray();
                    return;
                }

                let action = '';

                // Remove elements outside window
                while (deque.length > 0 && deque[0] < currentIndex - k + 1) {
                    const removed = deque.shift();
                    action += `Remove ${nums[removed]} (index ${removed}) - outside window. `;
                }

                // Remove smaller elements from back
                while (deque.length > 0 && nums[deque[deque.length - 1]] < nums[currentIndex]) {
                    const removed = deque.pop();
                    action += `Pop ${nums[removed]} (smaller than ${nums[currentIndex]}). `;
                }

                // Add current
                deque.push(currentIndex);
                action += `Add ${nums[currentIndex]} at index ${currentIndex}. `;

                // If window is full, record max
                if (currentIndex >= k - 1) {
                    result.push(nums[deque[0]]);
                    action += `Window full! Max = ${nums[deque[0]]}`;
                } else {
                    action += `Window not yet full (need ${k} elements)`;
                }

                document.getElementById('statusMessage').textContent = action;

                renderArray();
                renderDeque();
                renderResult();

                currentIndex++;
            }
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (phase === 'done') {
                        stopAuto();
                    } else {
                        step();
                    }
                }, 1500);
            }
        }

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

        function reset() {
            stopAuto();
            phase = 'init';
            currentIndex = 0;
            deque = [];
            result = [];
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').textContent =
                'Click "Step" or "Auto Run" to see how the monotonic deque finds maximums';
            init();
        }

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