algorithm-neet-code-top-150-python-visual/visual/0167_two_sum_ii.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>Two Sum II - LeetCode 167</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">#167</span> Two Sum II - Input Array Is Sorted</h1>
            <p>Given a sorted array and a target, find two numbers that add up to the target. Return their 1-indexed positions. The two-pointer technique makes this elegant!</p>
            <div class="problem-meta">
                <span class="meta-tag">👉👉 Two Pointers</span>
                <span class="meta-tag">📊 Sorted Array</span>
                <span class="meta-tag">⏱️ O(n)</span>
                <span class="meta-tag">💾 O(1)</span>
            </div>
            <div class="file-ref">
                📄 Python: <a href="../python/0167_two_sum_2/0167_two_sum_2.py">0167_two_sum_2.py</a>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>💡 How It Works (Layman's Terms)</h4>
            <ul>
                <li><strong>Key Insight:</strong> The array is SORTED! This changes everything.</li>
                <li><strong>Two Pointers:</strong> Start with one pointer at the beginning (smallest) and one at the end (largest)</li>
                <li><strong>Sum too big?</strong> Move the right pointer left to get a smaller number</li>
                <li><strong>Sum too small?</strong> Move the left pointer right to get a bigger number</li>
                <li><strong>Why it works:</strong> Because it's sorted, moving left makes sum smaller, moving right makes it bigger</li>
                <li><strong>Result:</strong> 1-indexed positions (add 1 to 0-indexed positions)</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" id="targetBox">
                Target Sum = 9
            </div>

            <div class="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to find two numbers that sum to target
            </div>

            <div class="variable-display">
                <div class="variable-box">
                    <div class="variable-name">Left Pointer</div>
                    <div class="variable-value" id="leftVal">0</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Right Pointer</div>
                    <div class="variable-value" id="rightVal">3</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Current Sum</div>
                    <div class="variable-value" id="sumVal">-</div>
                </div>
            </div>

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

            <div id="pointerContainer" style="margin-top: 10px;">
                <!-- Pointer indicators will be drawn here -->
            </div>
        </div>
        <div class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">twoSum</span>(self, numbers: <span class="class-name">List</span>[int], target: <span class="class-name">int</span>) -> List[int]:
    left = <span class="number">0</span>
    right = <span class="function">len</span>(numbers) - <span class="number">1</span>

    <span class="keyword">while</span> left < right:
        current_sum = numbers[left] + numbers[right]

        <span class="keyword">if</span> current_sum > target:
            right -= <span class="number">1</span>  <span class="comment"># Sum too big, need smaller</span>
        <span class="keyword">elif</span> current_sum < target:
            left += <span class="number">1</span>   <span class="comment"># Sum too small, need bigger</span>
        <span class="keyword">else</span>:
            <span class="keyword">return</span> [left + <span class="number">1</span>, right + <span class="number">1</span>]  <span class="comment"># 1-indexed</span>

    <span class="keyword">return</span> <span class="keyword">None</span></pre>
            </div>
        </div>

        </div>

    <script>
        const numbers = [2, 7, 11, 15];
        const target = 9;
        let left = 0;
        let right = numbers.length - 1;
        let phase = 'init';
        let autoInterval = null;

        function init() {
            renderArray();
            document.getElementById('leftVal').textContent = '0';
            document.getElementById('rightVal').textContent = (numbers.length - 1).toString();
            document.getElementById('sumVal').textContent = '-';
        }

        function renderArray() {
            const container = document.getElementById('arrayContainer');
            container.innerHTML = '';
            numbers.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>`;
                container.appendChild(box);
            });
            updatePointers();
        }

        function updatePointers() {
            document.querySelectorAll('.array-box').forEach(b => {
                b.classList.remove('pointer-left', 'pointer-right', 'complete');
            });

            if (left < numbers.length) {
                document.getElementById(`num-${left}`).classList.add('pointer-left');
            }
            if (right >= 0) {
                document.getElementById(`num-${right}`).classList.add('pointer-right');
            }

            // Draw pointer indicators
            const pointerContainer = document.getElementById('pointerContainer');
            const arrayContainer = document.getElementById('arrayContainer');
            const boxes = arrayContainer.getElementsByClassName('array-box');

            let html = '<div style="display: flex; gap: 8px; padding-left: 0;">';
            for (let i = 0; i < numbers.length; i++) {
                html += '<div style="width: 60px; text-align: center;">';
                if (i === left) {
                    html += '<span style="color: #ff5722; font-weight: bold;">↑ L</span>';
                } else if (i === right) {
                    html += '<span style="color: #3f51b5; font-weight: bold;">↑ R</span>';
                }
                html += '</div>';
            }
            html += '

        </div>';
            pointerContainer.innerHTML = html;
        }

        function step() {
            if (phase === 'init') {
                phase = 'searching';
                document.getElementById('statusMessage').textContent =
                    'Starting two-pointer search: left at smallest, right at largest';
            }

            if (phase === 'searching') {
                if (left >= right) {
                    phase = 'done';
                    document.getElementById('statusMessage').textContent = 'No solution found (pointers crossed)';
                    document.getElementById('stepBtn').disabled = true;
                    stopAuto();
                    return;
                }

                const sum = numbers[left] + numbers[right];
                document.getElementById('sumVal').textContent = sum.toString();
                document.getElementById('leftVal').textContent = left.toString();
                document.getElementById('rightVal').textContent = right.toString();

                if (sum === target) {
                    phase = 'done';
                    document.getElementById(`num-${left}`).classList.add('complete');
                    document.getElementById(`num-${right}`).classList.add('complete');
                    document.getElementById('statusMessage').textContent =
                        `✅ Found! numbers[${left}] + numbers[${right}] = ${numbers[left]} + ${numbers[right]} = ${target}. Answer: [${left + 1}, ${right + 1}] (1-indexed)`;
                    document.getElementById('stepBtn').disabled = true;
                    stopAuto();
                } else if (sum > target) {
                    document.getElementById('statusMessage').textContent =
                        `Sum ${sum} > target ${target} → Move RIGHT pointer left to get smaller number`;
                    right--;
                    updatePointers();
                } else {
                    document.getElementById('statusMessage').textContent =
                        `Sum ${sum} < target ${target} → Move LEFT pointer right to get bigger number`;
                    left++;
                    updatePointers();
                }
            }
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (phase === 'done') {
                        stopAuto();
                    } else {
                        step();
                    }
                }, 1200);
            }
        }

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

        function reset() {
            stopAuto();
            phase = 'init';
            left = 0;
            right = numbers.length - 1;
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').textContent =
                'Click "Step" or "Auto Run" to find two numbers that sum to target';
            init();
        }

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