algorithm-neet-code-top-150-python-visual/visual/0347_top_k_frequent_elements.html at main · kimtth/algorithm-neet-code-top-150-python-visual · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Top K Frequent Elements - LeetCode 347</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">#0347</span> Top K Frequent Elements</h1>
            <p><strong>Problem:</strong> Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.</p>
            <p><strong>Pattern:</strong> Bucket Sort (O(n) time complexity)</p>
            <p><strong>File:</strong> 0347_top_k_frequent_elements/0347_top_k_frequent_elements.py</p>
            <div class="problem-meta">
                <span class="meta-tag">⛰️ Heap</span>
                <span class="meta-tag">⏱️ O(n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <code>python/0347_top_k_frequent_elements/0347_top_k_frequent_elements.py</code>
            </div>

        </div>

        <div class="explanation-panel">
            <h4>🧠 How It Works (Layman's Terms)</h4>
            <p>A heap is like a <strong>priority queue</strong> - always access the best element:</p>
            <ul>
                <li><strong>Min heap:</strong> Smallest element always on top</li>
                <li><strong>Max heap:</strong> Largest element always on top</li>
                <li><strong>Insert/Remove:</strong> O(log n) to maintain order</li>
                <li><strong>Use case:</strong> Great for "top K" problems</li>
            </ul>
        </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" or "Auto Run" to begin</div>

        <div class="variables">
            <div class="var-item">
                <span class="var-label">Input:</span>
                <span id="inputDisplay">[1,1,1,2,2,3], k=2</span>
            </div>
            <div class="var-item">
                <span class="var-label">Phase:</span>
                <span id="phaseDisplay">Count Frequencies</span>
            </div>
            <div class="var-item">
                <span class="var-label">Result:</span>
                <span id="resultDisplay">[]</span>
            </div>
        </div>

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

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

        </div>

        <div class="code-section">
            <h3>Python Solution (Bucket Sort)</h3>
            <div class="code-block">
                <pre><span class="keyword">def</span> <span class="function">topKFrequent_bucket_sort</span>(nums, k):
    <span class="string">"""
    Find k most frequent elements using bucket sort.
    Time: O(n), Space: O(n)
    """</span>
    <span class="comment"># Step 1: Count frequencies</span>
    count = {}
    <span class="keyword">for</span> n <span class="keyword">in</span> nums:
        count[n] = count.<span class="function">get</span>(n, <span class="number">0</span>) + <span class="number">1</span>

    <span class="comment"># Step 2: Create frequency buckets (index = frequency)</span>
    freq = [[] <span class="keyword">for</span> _ <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(nums) + <span class="number">1</span>)]
    <span class="keyword">for</span> num, cnt <span class="keyword">in</span> count.<span class="function">items</span>():
        freq[cnt].<span class="function">append</span>(num)

    <span class="comment"># Step 3: Collect k elements from highest frequency buckets</span>
    result = []
    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(freq) - <span class="number">1</span>, <span class="number">0</span>, <span class="number">-1</span>):
        <span class="keyword">for</span> num <span class="keyword">in</span> freq[i]:
            result.<span class="function">append</span>(num)
            <span class="keyword">if</span> <span class="function">len</span>(result) == k:
                <span class="keyword">return</span> result
    <span class="keyword">return</span> result</pre>
            </div>
        </div>
    </div>

    <script>
        // Visualization state
        const nums = [1, 1, 1, 2, 2, 3];
        const k = 2;
        let count = {};
        let freq = [];
        let result = [];
        let phase = "counting"; // "counting", "bucketing", "collecting"
        let currentIndex = 0;
        let collectIndex = 0;
        let autoRunning = false;
        let autoTimer = null;

        // SVG setup
        const width = 850;
        const height = 450;
        const svg = d3.select("#mainSvg")
            .attr("width", width)
            .attr("height", height);

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

            const cellWidth = 50;
            const cellHeight = 40;

            // Draw input array
            svg.append("text")
                .attr("x", 30)
                .attr("y", 30)
                .attr("class", "section-title")
                .text("Input Array:");

            const inputStartX = 150;
            nums.forEach((num, i) => {
                const isHighlighted = phase === "counting" && i === currentIndex - 1;
                svg.append("rect")
                    .attr("x", inputStartX + i * cellWidth)
                    .attr("y", 15)
                    .attr("width", cellWidth - 4)
                    .attr("height", cellHeight)
                    .attr("rx", 5)
                    .attr("class", isHighlighted ? "cell current" : "cell");

                svg.append("text")
                    .attr("x", inputStartX + i * cellWidth + (cellWidth - 4) / 2)
                    .attr("y", 15 + cellHeight / 2)
                    .attr("dy", ".35em")
                    .attr("text-anchor", "middle")
                    .attr("class", "cell-text")
                    .text(num);
            });

            // Draw frequency count map
            svg.append("text")
                .attr("x", 30)
                .attr("y", 100)
                .attr("class", "section-title")
                .text("Frequency Count:");

            const countEntries = Object.entries(count);
            let countX = 180;
            countEntries.forEach(([num, cnt], i) => {
                svg.append("rect")
                    .attr("x", countX)
                    .attr("y", 80)
                    .attr("width", 80)
                    .attr("height", cellHeight)
                    .attr("rx", 5)
                    .attr("class", "cell count-cell");

                svg.append("text")
                    .attr("x", countX + 40)
                    .attr("y", 80 + cellHeight / 2)
                    .attr("dy", ".35em")
                    .attr("text-anchor", "middle")
                    .attr("class", "cell-text")
                    .text(`${num}→${cnt}`);

                countX += 90;
            });

            if (countEntries.length === 0) {
                svg.append("text")
                    .attr("x", 180)
                    .attr("y", 100)
                    .attr("class", "empty-text")
                    .text("{ empty }");
            }

            // Draw frequency buckets
            svg.append("text")
                .attr("x", 30)
                .attr("y", 170)
                .attr("class", "section-title")
                .text("Frequency Buckets:");

            const bucketY = 185;
            const bucketWidth = 100;
            const bucketHeight = 50;
            const maxFreq = nums.length;

            for (let i = 1; i <= maxFreq; i++) {
                const bucketX = 30 + (i - 1) * (bucketWidth + 10);
                const bucket = freq[i] || [];
                const isCollecting = phase === "collecting" && collectIndex === i;

                svg.append("rect")
                    .attr("x", bucketX)
                    .attr("y", bucketY)
                    .attr("width", bucketWidth)
                    .attr("height", bucketHeight)
                    .attr("rx", 5)
                    .attr("class", isCollecting ? "bucket current" : (bucket.length > 0 ? "bucket filled" : "bucket empty"));

                svg.append("text")
                    .attr("x", bucketX + bucketWidth / 2)
                    .attr("y", bucketY - 10)
                    .attr("text-anchor", "middle")
                    .attr("class", "bucket-label")
                    .text(`freq=${i}`);

                svg.append("text")
                    .attr("x", bucketX + bucketWidth / 2)
                    .attr("y", bucketY + bucketHeight / 2)
                    .attr("dy", ".35em")
                    .attr("text-anchor", "middle")
                    .attr("class", "bucket-text")
                    .text(bucket.length > 0 ? `[${bucket.join(", ")}]` : "[ ]");
            }

            // Draw result collection
            svg.append("text")
                .attr("x", 30)
                .attr("y", 300)
                .attr("class", "section-title")
                .text(`Result (need ${k} elements):`);

            const resultStartX = 230;
            if (result.length === 0) {
                svg.append("text")
                    .attr("x", resultStartX)
                    .attr("y", 300)
                    .attr("class", "empty-text")
                    .text("[ ]");
            } else {
                result.forEach((num, i) => {
                    svg.append("rect")
                        .attr("x", resultStartX + i * 60)
                        .attr("y", 280)
                        .attr("width", 50)
                        .attr("height", cellHeight)
                        .attr("rx", 5)
                        .attr("class", "cell result-cell");

                    svg.append("text")
                        .attr("x", resultStartX + i * 60 + 25)
                        .attr("y", 280 + cellHeight / 2)
                        .attr("dy", ".35em")
                        .attr("text-anchor", "middle")
                        .attr("class", "cell-text")
                        .text(num);
                });
            }

            // Arrow showing collection direction
            if (phase === "collecting") {
                svg.append("text")
                    .attr("x", width / 2)
                    .attr("y", 360)
                    .attr("text-anchor", "middle")
                    .attr("class", "direction-text")
                    .text("← Collecting from highest frequency to lowest");
            }

            // Final result
            if (result.length === k) {
                svg.append("text")
                    .attr("x", width / 2)
                    .attr("y", 400)
                    .attr("text-anchor", "middle")
                    .attr("class", "result-final")
                    .text(`✓ Found ${k} most frequent: [${result.join(", ")}]`);
            }
        }

        function step() {
            if (phase === "counting") {
                if (currentIndex >= nums.length) {
                    phase = "bucketing";
                    currentIndex = 0;
                    // Initialize frequency buckets
                    freq = Array.from({length: nums.length + 1}, () => []);
                    document.getElementById("phaseDisplay").textContent = "Create Buckets";
                    document.getElementById("status").textContent = "Counting done! Now creating frequency buckets...";
                    highlightCode("freq = [[] for");
                    drawVisualization();
                    return true;
                }

                const num = nums[currentIndex];
                count[num] = (count[num] || 0) + 1;
                currentIndex++;

                document.getElementById("status").textContent =
                    `Counting: nums[${currentIndex - 1}] = ${num}, count[${num}] = ${count[num]}`;
                highlightCode("count[n] = count.get");
                drawVisualization();
                return true;
            } else if (phase === "bucketing") {
                const entries = Object.entries(count);
                if (currentIndex >= entries.length) {
                    phase = "collecting";
                    collectIndex = nums.length;
                    document.getElementById("phaseDisplay").textContent = "Collect Top K";
                    document.getElementById("status").textContent = "Buckets created! Now collecting k most frequent from highest frequency...";
                    highlightCode("for i in range(len(freq) - 1");
                    drawVisualization();
                    return true;
                }

                const [num, cnt] = entries[currentIndex];
                freq[cnt].push(parseInt(num));
                currentIndex++;

                document.getElementById("status").textContent =
                    `Bucketing: ${num} has frequency ${cnt}, adding to bucket[${cnt}]`;
                highlightCode("freq[cnt].append(num)");
                drawVisualization();
                return true;
            } else if (phase === "collecting") {
                if (result.length >= k) {
                    document.getElementById("status").textContent = `Done! Top ${k} frequent elements: [${result.join(", ")}]`;
                    document.getElementById("resultDisplay").textContent = `[${result.join(", ")}]`;
                    highlightCode("return result");
                    drawVisualization();
                    return false;
                }

                // Find next non-empty bucket from high to low
                while (collectIndex > 0 && (freq[collectIndex] || []).length === 0) {
                    collectIndex--;
                }

                if (collectIndex <= 0) {
                    document.getElementById("status").textContent = "No more elements!";
                    return false;
                }

                const bucket = freq[collectIndex];
                if (bucket.length > 0) {
                    const num = bucket.shift();
                    result.push(num);
                    document.getElementById("status").textContent =
                        `Collecting: Taking ${num} from bucket[${collectIndex}], result = [${result.join(", ")}]`;
                    document.getElementById("resultDisplay").textContent = `[${result.join(", ")}]`;
                    highlightCode("result.append(num)");
                }

                if (bucket.length === 0) {
                    collectIndex--;
                }

                drawVisualization();
                return result.length < k;
            }
            return false;
        }

        function highlightCode(text) {
            const codeDisplay = document.getElementById("codeDisplay");
            const code = codeDisplay.textContent;
            const highlighted = code.replace(
                new RegExp(`(.*${text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}.*)`),
                '<span class="highlight-line">$1</span>'
            );
            codeDisplay.innerHTML = highlighted;
        }

        function reset() {
            count = {};
            freq = [];
            result = [];
            phase = "counting";
            currentIndex = 0;
            collectIndex = 0;
            autoRunning = false;
            if (autoTimer) {
                clearInterval(autoTimer);
                autoTimer = null;
            }

            document.getElementById("phaseDisplay").textContent = "Count Frequencies";
            document.getElementById("resultDisplay").textContent = "[]";
            document.getElementById("status").textContent = 'Click "Step" or "Auto Run" to begin';
            document.getElementById("autoBtn").textContent = "Auto Run";

            drawVisualization();
            document.getElementById("codeDisplay").innerHTML = document.getElementById("codeDisplay").textContent;
        }

        function autoRun() {
            if (autoRunning) {
                autoRunning = false;
                clearInterval(autoTimer);
                autoTimer = null;
                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);
                        autoTimer = null;
                        document.getElementById("autoBtn").textContent = "Auto Run";
                    }
                }, speed);
            }
        }

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

        // Initialize
        drawVisualization();
    </script>

    <style>
        .section-title {
            font-size: 14px;
            font-weight: bold;
            fill: #333;
        }
        .cell {
            fill: #e3f2fd;
            stroke: #1976d2;
            stroke-width: 2;
        }
        .cell.current {
            fill: #fff3e0;
            stroke: #f57c00;
            stroke-width: 3;
        }
        .count-cell {
            fill: #f3e5f5;
            stroke: #7b1fa2;
        }
        .result-cell {
            fill: #c8e6c9;
            stroke: #388e3c;
            stroke-width: 2;
        }
        .bucket {
            stroke-width: 2;
        }
        .bucket.empty {
            fill: #f5f5f5;
            stroke: #bdbdbd;
        }
        .bucket.filled {
            fill: #e8f5e9;
            stroke: #4caf50;
        }
        .bucket.current {
            fill: #fff3e0;
            stroke: #f57c00;
            stroke-width: 3;
        }
        .cell-text {
            font-size: 14px;
            font-weight: bold;
            fill: #333;
        }
        .bucket-label {
            font-size: 11px;
            fill: #666;
        }
        .bucket-text {
            font-size: 12px;
            fill: #333;
        }
        .empty-text {
            font-size: 14px;
            fill: #999;
            font-style: italic;
        }
        .direction-text {
            font-size: 14px;
            fill: #666;
        }
        .result-final {
            font-size: 18px;
            font-weight: bold;
            fill: #388e3c;
        }
    </style>
</body>
</html>