algorithm-neet-code-top-150-python-visual/visual/0115_distinct_subsequences.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>115 - Distinct Subsequences</title>
    <link rel="stylesheet" href="styles.css">
    <script src="https://d3js.org/d3.v7.min.js"></script>
    <style>
        .string-display { display: flex; justify-content: center; gap: 5px; margin: 15px 0; flex-wrap: wrap; }
        .char-box { width: 40px; height: 50px; display: flex; flex-direction: column; align-items: center; justify-content: center; border-radius: 8px; font-size: 1.2rem; font-weight: bold; transition: all 0.3s ease; }
        .char-box.source { background: linear-gradient(135deg, #6366f1, #8b5cf6); color: white; }
        .char-box.target { background: linear-gradient(135deg, #10b981, #34d399); color: white; }
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        input:focus { outline: none; border-color: #6366f1; }
    </style>
</head>
<body>
    <div class="container">
        <section class="problem-info">
            <h1><span class="problem-number">#115</span> Distinct Subsequences</h1>
            <p>Count the number of distinct subsequences of string s that equal string t. A subsequence is formed by deleting some (or none) characters without changing the relative order of remaining characters.</p>
            <div class="problem-meta">
                <span class="meta-tag">Hard</span>
                <span class="meta-tag">Dynamic Programming</span>
                <span class="meta-tag">String</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0115_distinct_subsequences/0115_distinct_subsequences.py</code>
            </div>

        </section>

        <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>


        <section class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>
            <div class="controls">
                <label>s: <input type="text" id="sInput" value="rabbbit"></label>
                <label>t: <input type="text" id="tInput" value="rabbit"></label>
                <button onclick="setInputs()">Set</button>
                <button id="stepBtn" onclick="step()">Step</button>
                <button id="autoBtn" onclick="toggleAuto()">▶ Auto Run</button>
                <button onclick="reset()">Reset</button>
            </div>
        </section>

        <section class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>
            <div>
                <div style="text-align: center; margin-bottom: 5px; color: #64748b;">Source string s:</div>
                <div class="string-display" id="sDisplay"></div>
            </div>
            <div style="margin-top: 15px;">
                <div style="text-align: center; margin-bottom: 5px; color: #64748b;">Target string t:</div>
                <div class="string-display" id="tDisplay"></div>
            </div>
        </section>

        <section class="visualization-section">
            <h3>🎬 Step-by-Step Visualization</h3>
            <div class="formula">
                If s[i-1] == t[j-1]: dp[i][j] = dp[i-1][j-1] + dp[i-1][j]<br>
                Else: dp[i][j] = dp[i-1][j]
            </div>
            <div id="dpTable"></div>
            <div class="status-message" id="stepDisplay">Ready to start</div>
            <div id="resultArea"></div>
        </section>

        <section class="code-section">
            <h3>💻 Python Solution</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">numDistinct</span>(s: <span class="class-name">str</span>, t: <span class="class-name">str</span>) -> int:
    m, n = <span class="function">len</span>(s), <span class="function">len</span>(t)

    <span class="comment"># dp[i][j] = number of ways to form t[0:j] from s[0:i]</span>
    dp = [[<span class="number">0</span>] * (n + <span class="number">1</span>) <span class="keyword">for</span> _ <span class="keyword">in</span> <span class="function">range</span>(m + <span class="number">1</span>)]

    <span class="comment"># Empty t can be formed from any prefix of s in 1 way</span>
    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(m + <span class="number">1</span>):
        dp[i][<span class="number">0</span>] = <span class="number">1</span>

    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="number">1</span>, m + <span class="number">1</span>):
        <span class="keyword">for</span> j <span class="keyword">in</span> <span class="function">range</span>(<span class="number">1</span>, n + <span class="number">1</span>):
            <span class="comment"># Always inherit: skip s[i-1]</span>
            dp[i][j] = dp[i-<span class="number">1</span>][j]

            <span class="comment"># If characters match, also add ways using s[i-1]</span>
            <span class="keyword">if</span> s[i-<span class="number">1</span>] == t[j-<span class="number">1</span>]:
                dp[i][j] += dp[i-<span class="number">1</span>][j-<span class="number">1</span>]

    <span class="keyword">return</span> dp[m][n]</pre>
            </div>
        </section>
    </div>

    <script>
        let s = "rabbbit";
        let t = "rabbit";
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            s = document.getElementById('sInput').value;
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                    let matchVal = 0;

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                    const newVal = skipVal + matchVal;
                    let desc, type;
                    if (s[i-1] === t[j-1]) {
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                isComplete = true;
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            stepIndex++;
            render();
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                }, 300);
                document.getElementById('autoBtn').textContent = '⏸ Pause';
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        }

        function render() {
            const m = s.length, n = t.length;
            const curStep = stepIndex > 0 ? steps[stepIndex - 1] : null;
            const curI = curStep?.i ?? -1;
            const curJ = curStep?.j ?? -1;

            let sHtml = '';
            for (let i = 0; i < s.length; i++) {
                const isCurrent = curI === i + 1;
                sHtml += `<div class="char-box source ${isCurrent ? 'current' : ''}"><span>${s[i]}</span><span class="idx">${i}</span></div>`;
            }
            document.getElementById('sDisplay').innerHTML = sHtml;

            let tHtml = '';
            for (let j = 0; j < t.length; j++) {
                const isCurrent = curJ === j + 1;
                tHtml += `<div class="char-box target ${isCurrent ? 'current' : ''}"><span>${t[j]}</span><span class="idx">${j}</span></div>`;
            }
            document.getElementById('tDisplay').innerHTML = tHtml;

            let tableHtml = '<table><tr><th></th><th>ε</th>';
            for (let j = 0; j < n; j++) tableHtml += `<th>${t[j]}</th>`;
            tableHtml += '</tr>';

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                tableHtml += `<tr><th>${i === 0 ? 'ε' : s[i-1]}</th>`;
                for (let j = 0; j <= n; j++) {
                    const isCurrent = curI === i && curJ === j;
                    const hasValue = dp[i][j] > 0;
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            if (isComplete) {
                document.getElementById('resultArea').innerHTML = `<div class="result">🎯 Number of distinct subsequences: <strong>${dp[m][n]}</strong></div>`;
            } else {
                document.getElementById('resultArea').innerHTML = '';
            }
        }

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