algorithm-neet-code-top-150-python-visual/visual/0015_3_sum.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 15: 3Sum - 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">#15</span> 3Sum</h1>
            <p>Given an integer array nums, return all unique triplets [nums[i], nums[j], nums[k]] where i ≠ j ≠ k and nums[i] + nums[j] + nums[k] == 0.</p>
            <div class="problem-meta">
                <span class="meta-tag">📁 Array</span>
                <span class="meta-tag">👉👈 Two Pointers</span>
                <span class="meta-tag">📊 Sorting</span>
                <span class="meta-tag">⏱️ O(n²)</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0015_3_sum/0015_3_sum.py</code>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>We want to find three numbers that add up to zero. The trick is:</p>
            <ul>
                <li><strong>Sort first:</strong> This lets us use two pointers efficiently</li>
                <li><strong>Fix one number:</strong> For each number, find two others that complete the sum</li>
                <li><strong>Two pointers:</strong> After fixing one number, use left/right pointers on the rest</li>
                <li><strong>Adjust pointers:</strong> If sum too small → move left up. If too big → move right down</li>
                <li><strong>Skip duplicates:</strong> To avoid duplicate triplets</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="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to start visualization
            </div>

            <div class="variable-display">
                <div class="variable-box">
                    <div class="variable-name">Fixed (i)</div>
                    <div class="variable-value" id="fixedVal" style="color: #9c27b0;">-</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Left</div>
                    <div class="variable-value" id="leftVal" style="color: #ff5722;">-</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Right</div>
                    <div class="variable-value" id="rightVal" style="color: #3f51b5;">-</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Sum</div>
                    <div class="variable-value" id="sumVal">-</div>
                </div>
            </div>

            <div class="array-section">
                <div class="array-label">📥 Sorted Array:</div>
                <div class="array-container" id="arrayContainer"></div>
            </div>

            <div class="array-section">
                <div class="array-label">✅ Found Triplets:</div>
                <div id="tripletsContainer">
                    <div style="color: #999; padding: 10px;">No triplets found yet</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">three_sum</span>(self, nums: <span class="class-name">List</span>[int]) -> List[List[int]]:
    nums.<span class="function">sort</span>()
    result = []

    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(nums) - <span class="number">2</span>):
        <span class="keyword">if</span> i > <span class="number">0</span> <span class="keyword">and</span> nums[i] == nums[i-<span class="number">1</span>]:
            <span class="keyword">continue</span>  <span class="comment"># Skip duplicates</span>

        left, right = i + <span class="number">1</span>, <span class="function">len</span>(nums) - <span class="number">1</span>

        <span class="keyword">while</span> left < right:
            total = nums[i] + nums[left] + nums[right]

            <span class="keyword">if</span> total < <span class="number">0</span>:
                left += <span class="number">1</span>
            <span class="keyword">elif</span> total > <span class="number">0</span>:
                right -= <span class="number">1</span>
            <span class="keyword">else</span>:
                result.<span class="function">append</span>([nums[i], nums[left], nums[right]])
                <span class="comment"># Skip duplicates</span>
                <span class="keyword">while</span> left < right <span class="keyword">and</span> nums[left] == nums[left+<span class="number">1</span>]: <span class="class-name">left</span> += <span class="number">1</span>
                <span class="keyword">while</span> left < right <span class="keyword">and</span> nums[right] == nums[right-<span class="number">1</span>]: <span class="class-name">right</span> -= <span class="number">1</span>
                left += <span class="number">1</span>
                right -= <span class="number">1</span>

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

    <script>
        const originalNums = [-1, 0, 1, 2, -1, -4];
        const nums = [...originalNums].sort((a, b) => a - b);
        let i = 0, left = 1, right = nums.length - 1;
        let triplets = [];
        let phase = 'init';
        let autoInterval = null;

        function init() {
            renderArray();
            document.getElementById('fixedVal').textContent = '-';
            document.getElementById('leftVal').textContent = '-';
            document.getElementById('rightVal').textContent = '-';
            document.getElementById('sumVal').textContent = '-';
        }

        function renderArray() {
            const container = document.getElementById('arrayContainer');
            container.innerHTML = '';
            nums.forEach((num, idx) => {
                const box = document.createElement('div');
                box.className = 'array-box';
                box.id = `arr-${idx}`;
                box.innerHTML = `${num}<span class="index-label">[${idx}]</span>`;

                if (idx === i) {
                    box.style.background = '#e1bee7';
                    box.style.borderColor = '#9c27b0';
                }
                if (idx === left && phase !== 'init') {
                    box.style.background = '#ffccbc';
                    box.style.borderColor = '#ff5722';
                }
                if (idx === right && phase !== 'init') {
                    box.style.background = '#c5cae9';
                    box.style.borderColor = '#3f51b5';
                }

                container.appendChild(box);
            });
        }

        function renderTriplets() {
            const container = document.getElementById('tripletsContainer');
            if (triplets.length === 0) {
                container.innerHTML = '<div style="color: #999; padding: 10px;">No triplets found yet</div>';
                return;
            }
            container.innerHTML = '';
            triplets.forEach((triplet, idx) => {
                const tripletDiv = document.createElement('div');
                tripletDiv.style.cssText = 'display: inline-block; padding: 10px 20px; background: #e8f5e9; border: 2px solid #4caf50; border-radius: 8px; margin: 5px; font-weight: bold;';
                tripletDiv.textContent = `[${triplet.join(', ')}]`;
                container.appendChild(tripletDiv);
            });
        }

        function step() {
            if (i >= nums.length - 2) {
                document.getElementById('statusMessage').className = 'status-message success';
                document.getElementById('statusMessage').textContent =
                    `✅ Done! Found ${triplets.length} unique triplet(s).`;
                document.getElementById('stepBtn').disabled = true;
                stopAuto();
                return;
            }

            if (phase === 'init') {
                phase = 'searching';
                left = i + 1;
                right = nums.length - 1;
            }

            // Skip duplicate i values
            if (i > 0 && nums[i] === nums[i - 1]) {
                document.getElementById('statusMessage').textContent =
                    `Skipping duplicate fixed value: ${nums[i]}`;
                i++;
                left = i + 1;
                right = nums.length - 1;
                renderArray();
                return;
            }

            document.getElementById('fixedVal').textContent = nums[i];
            document.getElementById('leftVal').textContent = nums[left];
            document.getElementById('rightVal').textContent = nums[right];

            if (left >= right) {
                // Move to next i
                i++;
                left = i + 1;
                right = nums.length - 1;
                document.getElementById('statusMessage').textContent =
                    `Pointers crossed. Moving to next fixed value.`;
                renderArray();
                return;
            }

            const total = nums[i] + nums[left] + nums[right];
            document.getElementById('sumVal').textContent = total;

            if (total < 0) {
                document.getElementById('statusMessage').textContent =
                    `Sum = ${nums[i]} + ${nums[left]} + ${nums[right]} = ${total} < 0. Move left →`;
                left++;
            } else if (total > 0) {
                document.getElementById('statusMessage').textContent =
                    `Sum = ${nums[i]} + ${nums[left]} + ${nums[right]} = ${total} > 0. Move right ←`;
                right--;
            } else {
                // Found a triplet!
                triplets.push([nums[i], nums[left], nums[right]]);
                renderTriplets();
                document.getElementById('statusMessage').className = 'status-message success';
                document.getElementById('statusMessage').textContent =
                    `🎯 Found triplet: [${nums[i]}, ${nums[left]}, ${nums[right]}]!`;

                // Skip duplicates
                while (left < right && nums[left] === nums[left + 1]) left++;
                while (left < right && nums[right] === nums[right - 1]) right--;
                left++;
                right--;
            }

            renderArray();
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (i >= nums.length - 2) {
                        step();
                        stopAuto();
                    } else {
                        step();
                    }
                }, 1000);
            }
        }

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

        function reset() {
            stopAuto();
            i = 0;
            left = 1;
            right = nums.length - 1;
            triplets = [];
            phase = 'init';
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').className = 'status-message';
            document.getElementById('statusMessage').textContent = 'Click "Step" or "Auto Run" to start visualization';
            document.getElementById('tripletsContainer').innerHTML = '<div style="color: #999; padding: 10px;">No triplets found yet

        </div>';
            init();
        }

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