algorithm-neet-code-top-150-python-visual/visual/0268_missing_number.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>Missing Number - LeetCode 268</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">#0268</span> Missing Number</h1>
            <p><strong>Problem:</strong> Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.</p>
            <p><strong>Pattern:</strong> Bit Manipulation / Math - XOR or sum formula approach</p>
            <div class="problem-meta">
                <span class="meta-tag">📊 Array</span>
                <span class="meta-tag">💻 Bit</span>
                <span class="meta-tag">⏱️ O(n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0268_missing_number/0268_missing_number.py</code>
            </div>

        </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>This algorithm solves the problem <strong>step by step</strong>:</p>
            <ul>
                <li><strong>Understand:</strong> Parse the input data</li>
                <li><strong>Process:</strong> Apply the core logic</li>
                <li><strong>Optimize:</strong> Use efficient data structures</li>
                <li><strong>Return:</strong> Output the computed result</li>
            </ul>
        </div>


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

            <div class="visualization">
            <svg id="mainSvg"></svg>
        </div>

        <div class="controls">
            <button id="stepBtn">Step</button>
            <button id="autoBtn">Auto Run</button>
            <button id="resetBtn">Reset</button>
            <div class="speed-control">
                <label for="speed">Speed:</label>
                <input type="range" id="speed" min="100" max="2000" value="800">
            </div>
        </div>

        <div class="status" id="status">Click "Step" to find the missing number using XOR</div>

        <div class="variables">
            <div class="var-item">
                <span class="var-label">XOR with indices:</span>
                <span id="indexXor">0</span>
            </div>
            <div class="var-item">
                <span class="var-label">XOR with values:</span>
                <span id="valueXor">0</span>
            </div>
            <div class="var-item">
                <span class="var-label">Missing Number:</span>
                <span id="resultDisplay">-</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">missingNumber</span>(nums):
    <span class="string">"""
    XOR all indices (0 to n) with all values.
    Pairs cancel out, leaving the missing number.
    Time: O(n), Space: O(1)
    """</span>
    n = <span class="function">len</span>(nums)
    result = n  <span class="comment"># Start with n (last index)</span>

    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(n):
        result ^= i ^ nums[i]

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

    <script>
        const nums = [3, 0, 1];
        const n = nums.length;
        let phase = 0; // 0: init, 1-n: processing each index
        let result = n;
        let autoRunning = false;
        let autoTimer = null;

        const width = 800;
        const height = 400;
        const svg = d3.select("#mainSvg")
            .attr("width", width)
            .attr("height", height);

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

            // Array section
            svg.append("text")
                .attr("x", width / 2)
                .attr("y", 30)
                .attr("text-anchor", "middle")
                .attr("font-weight", "bold")
                .text(`nums = [${nums.join(", ")}], n = ${n}`);

            // Draw array
            const cellWidth = 70;
            const startX = (width - nums.length * cellWidth) / 2;

            const cells = svg.selectAll(".array-cell")
                .data(nums)
                .enter()
                .append("g")
                .attr("transform", (d, i) => `translate(${startX + i * cellWidth}, 50)`);

            cells.append("rect")
                .attr("width", cellWidth - 4)
                .attr("height", 50)
                .attr("rx", 5)
                .attr("class", "cell")
                .attr("id", (d, i) => `cell-${i}`);

            cells.append("text")
                .attr("x", (cellWidth - 4) / 2)
                .attr("y", 25)
                .attr("dy", ".35em")
                .attr("text-anchor", "middle")
                .attr("class", "cell-text")
                .text(d => d);

            cells.append("text")
                .attr("x", (cellWidth - 4) / 2)
                .attr("y", 70)
                .attr("text-anchor", "middle")
                .attr("class", "index-label")
                .text((d, i) => `i=${i}`);

            // Expected range
            svg.append("text")
                .attr("x", width / 2)
                .attr("y", 140)
                .attr("text-anchor", "middle")
                .attr("fill", "#666")
                .text(`Expected range: [0, 1, 2, 3] but one is missing!`);

            // XOR visualization
            svg.append("text")
                .attr("x", width / 2)
                .attr("y", 180)
                .attr("text-anchor", "middle")
                .attr("font-weight", "bold")
                .text("XOR Operation: result = n");

            // Result box
            svg.append("rect")
                .attr("x", width / 2 - 80)
                .attr("y", 320)
                .attr("width", 160)
                .attr("height", 50)
                .attr("rx", 8)
                .attr("id", "resultBox")
                .attr("fill", "#e3f2fd")
                .attr("stroke", "#1976d2")
                .attr("stroke-width", 2);

            svg.append("text")
                .attr("x", width / 2)
                .attr("y", 350)
                .attr("text-anchor", "middle")
                .attr("font-size", "20px")
                .attr("font-weight", "bold")
                .attr("id", "resultText")
                .text(`result = ${result}`);

            updateXORSteps();
        }

        function updateXORSteps() {
            svg.selectAll(".xor-step").remove();

            const stepGroup = svg.append("g")
                .attr("class", "xor-step")
                .attr("transform", `translate(${width/2 - 150}, 200)`);

            stepGroup.append("text")
                .attr("y", 0)
                .attr("font-family", "monospace")
                .text(`Start: result = ${n} (n)`);

            for (let i = 0; i < phase && i < n; i++) {
                stepGroup.append("text")
                    .attr("y", 25 * (i + 1))
                    .attr("font-family", "monospace")
                    .attr("fill", i === phase - 1 ? "#f57c00" : "#333")
                    .text(`XOR with i=${i}, nums[${i}]=${nums[i]}`);
            }
        }

        function step() {
            if (phase >= n) return false;

            // XOR with current index and value
            result ^= phase ^ nums[phase];

            document.getElementById("indexXor").textContent =
                Array.from({length: phase + 1}, (_, i) => i).join(" ⊕ ");
            document.getElementById("valueXor").textContent =
                nums.slice(0, phase + 1).join(" ⊕ ");

            // Highlight current cell
            svg.selectAll(".cell").attr("class", "cell");
            svg.select(`#cell-${phase}`).attr("class", "cell current");

            for (let i = 0; i < phase; i++) {
                svg.select(`#cell-${i}`).attr("class", "cell processed");
            }

            svg.select("#resultText").text(`result = ${result}`);

            phase++;
            updateXORSteps();

            if (phase >= n) {
                document.getElementById("resultDisplay").textContent = result;
                document.getElementById("status").textContent =
                    `Complete! The missing number is ${result}`;
                svg.select("#resultBox")
                    .attr("fill", "#c8e6c9")
                    .attr("stroke", "#4caf50");
                return false;
            } else {
                document.getElementById("status").textContent =
                    `Processing index ${phase - 1}: result = ${result}`;
                return true;
            }
        }

        function reset() {
            phase = 0;
            result = n;
            autoRunning = false;
            if (autoTimer) clearInterval(autoTimer);

            document.getElementById("indexXor").textContent = "0";
            document.getElementById("valueXor").textContent = "0";
            document.getElementById("resultDisplay").textContent = "-";
            document.getElementById("status").textContent = 'Click "Step" to find the missing number using XOR';
            document.getElementById("autoBtn").textContent = "Auto Run";

            drawVisualization();
        }

        function autoRun() {
            if (autoRunning) {
                autoRunning = false;
                clearInterval(autoTimer);
                document.getElementById("autoBtn").textContent = "Auto Run";
            } else {
                autoRunning = true;
                document.getElementById("autoBtn").textContent = "Pause";
                const speed = 2100 - document.getElementById("speed").value;
                autoTimer = setInterval(() => {
                    if (!step()) {
                        autoRunning = false;
                        clearInterval(autoTimer);
                        document.getElementById("autoBtn").textContent = "Auto Run";
                    }
                }, speed);
            }
        }

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

        drawVisualization();
    </script>

    <style>
        .cell { fill: #e3f2fd; stroke: #1976d2; stroke-width: 2; }
        .cell.current { fill: #fff3e0; stroke: #f57c00; stroke-width: 3; }
        .cell.processed { fill: #e8f5e9; stroke: #4caf50; stroke-width: 2; }
        .cell-text { font-size: 20px; font-weight: bold; fill: #333; }
        .index-label { font-size: 12px; fill: #666; }
    </style>
</body>
</html>