algorithm-neet-code-top-150-python-visual/visual/0853_car_fleet.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
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Car Fleet - LeetCode 853</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">#853</span> Car Fleet</h1>
            <p>Cars on a road heading to a target. Faster cars can't pass slower ones, they form "fleets." Count how many fleets reach the destination!</p>
            <div class="problem-meta">
                <span class="meta-tag">📚 Stack</span>
                <span class="meta-tag">🔢 Sorting</span>
                <span class="meta-tag">⏱️ O(n log n)</span>
            </div>
            <div class="file-ref">
                📄 Python: <a href="../python/0853_car_fleet/0853_car_fleet.py">0853_car_fleet.py</a>
            </div>
            </div>

        <div class="explanation-panel">
            <h4>💡 How It Works (Layman's Terms)</h4>
            <ul>
                <li><strong>Problem:</strong> Cars can't pass each other on a single-lane road. Faster cars behind slow down to match slower cars ahead.</li>
                <li><strong>Fleet:</strong> Cars that catch up and travel together at the same speed.</li>
                <li><strong>Key insight:</strong> Process cars from closest to target first. A car forms a new fleet if it takes longer to reach target than any car ahead.</li>
                <li><strong>Time to target:</strong> (target - position) / speed</li>
                <li><strong>Logic:</strong> If a car takes MORE time than the max time seen so far, it can't catch up → new fleet!</li>
                <li><strong>If LESS time:</strong> It would catch up and merge with the fleet ahead.</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">
                Target = 12 miles
            </div>

            <div class="status-message" id="statusMessage">
                Click "Step" or "Auto Run" to see how cars form fleets
            </div>

            <div class="svg-container">
                <svg id="roadSvg" width="800" height="200"></svg>
            </div>

            <div class="array-section">
                <div class="array-label">Cars (sorted by position, closest to target first):</div>
                <div id="carsTable" style="overflow-x: auto;"></div>
            </div>

            <div class="variable-display">
                <div class="variable-box">
                    <div class="variable-name">Current Max Time</div>
                    <div class="variable-value" id="maxTimeVal">0</div>
                </div>
                <div class="variable-box">
                    <div class="variable-name">Fleet Count</div>
                    <div class="variable-value" id="fleetVal">0</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">carFleet</span>(self, target: <span class="class-name">int</span>, position: List[<span class="class-name">int</span>], speed: List[<span class="class-name">int</span>]) -> <span class="class-name">int</span>:
    <span class="comment"># Create pairs of (position, time_to_target)</span>
    cars = []
    <span class="keyword">for</span> i <span class="keyword">in</span> <span class="function">range</span>(<span class="function">len</span>(position)):
        time = (target - position[i]) / speed[i]
        cars.append([position[i], time])

    <span class="comment"># Sort by position descending (closest to target first)</span>
    cars.<span class="function">sort</span>(reverse=<span class="class-name">True</span>)

    fleets = <span class="number">0</span>
    current_max_time = <span class="number">0</span>

    <span class="keyword">for</span> pos, time <span class="keyword">in</span> cars:
        <span class="keyword">if</span> time > current_max_time:
            fleets += <span class="number">1</span>
            current_max_time = time

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

    <script>
        const target = 12;
        const positions = [10, 8, 0, 5, 3];
        const speeds = [2, 4, 1, 1, 3];

        let cars = [];
        let sortedCars = [];
        let currentCarIndex = 0;
        let currentMaxTime = 0;
        let fleets = 0;
        let phase = 'init';
        let autoInterval = null;

        function init() {
            cars = positions.map((pos, i) => ({
                position: pos,
                speed: speeds[i],
                time: (target - pos) / speeds[i],
                fleet: null
            }));
            sortedCars = [...cars].sort((a, b) => b.position - a.position);
            currentCarIndex = 0;
            currentMaxTime = 0;
            fleets = 0;

            drawRoad();
            renderCarsTable();
            document.getElementById('maxTimeVal').textContent = '0';
            document.getElementById('fleetVal').textContent = '0';
        }

        function drawRoad() {
            const svg = d3.select("#roadSvg");
            svg.selectAll("*").remove();

            const roadY = 100;
            const roadStart = 50;
            const roadEnd = 750;
            const scale = (roadEnd - roadStart) / target;

            // Draw road
            svg.append("line")
                .attr("x1", roadStart)
                .attr("y1", roadY)
                .attr("x2", roadEnd)
                .attr("y2", roadY)
                .attr("stroke", "#333")
                .attr("stroke-width", 4);

            // Draw target
            svg.append("rect")
                .attr("x", roadEnd - 5)
                .attr("y", roadY - 30)
                .attr("width", 10)
                .attr("height", 60)
                .attr("fill", "#f44336");

            svg.append("text")
                .attr("x", roadEnd)
                .attr("y", roadY - 40)
                .attr("text-anchor", "middle")
                .attr("font-weight", "bold")
                .text("TARGET");

            // Draw cars
            const fleetColors = ['#667eea', '#11998e', '#f093fb', '#ff9800', '#4caf50'];

            sortedCars.forEach((car, i) => {
                const x = roadStart + car.position * scale;
                const color = car.fleet !== null ? fleetColors[car.fleet % fleetColors.length] : '#999';

                // Car body
                svg.append("rect")
                    .attr("x", x - 15)
                    .attr("y", roadY - 25)
                    .attr("width", 30)
                    .attr("height", 20)
                    .attr("rx", 5)
                    .attr("fill", color)
                    .attr("stroke", i === currentCarIndex && phase === 'processing' ? "#f44336" : "none")
                    .attr("stroke-width", 3);

                // Car info
                svg.append("text")
                    .attr("x", x)
                    .attr("y", roadY + 30)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "10px")
                    .text(`pos:${car.position}`);

                svg.append("text")
                    .attr("x", x)
                    .attr("y", roadY + 42)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "10px")
                    .text(`spd:${car.speed}`);

                svg.append("text")
                    .attr("x", x)
                    .attr("y", roadY + 54)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "10px")
                    .text(`t:${car.time.toFixed(1)}`);
            });

            // Position markers
            for (let p = 0; p <= target; p += 2) {
                const x = roadStart + p * scale;
                svg.append("text")
                    .attr("x", x)
                    .attr("y", roadY + 70)
                    .attr("text-anchor", "middle")
                    .attr("font-size", "10px")
                    .attr("fill", "#666")
                    .text(p);
            }
        }

        function renderCarsTable() {
            const container = document.getElementById('carsTable');
            let html = '<table class="problem-table"><tr><th>Order</th><th>Position</th><th>Speed</th><th>Time to Target</th><th>Fleet</th></tr>';

            sortedCars.forEach((car, i) => {
                const highlight = i === currentCarIndex && phase === 'processing' ? 'style="background: #fff3e0;"' : '';
                const fleetDisplay = car.fleet !== null ? `Fleet ${car.fleet + 1}` : '-';
                html += `<tr ${highlight}>
                    <td>${i + 1}</td>
                    <td>${car.position}</td>
                    <td>${car.speed}</td>
                    <td>${car.time.toFixed(2)}</td>
                    <td>${fleetDisplay}</td>
                </tr>`;
            });

            html += '</table>';
            container.innerHTML = html;
        }

        function step() {
            if (phase === 'init') {
                phase = 'processing';
                document.getElementById('statusMessage').textContent =
                    'Processing cars from closest to target (position 10) to farthest...';
            }

            if (phase === 'processing') {
                if (currentCarIndex >= sortedCars.length) {
                    phase = 'done';
                    document.getElementById('statusMessage').textContent =
                        `✅ Done! Total fleets: ${fleets}`;
                    document.getElementById('stepBtn').disabled = true;
                    stopAuto();
                    return;
                }

                const car = sortedCars[currentCarIndex];

                if (car.time > currentMaxTime) {
                    // New fleet!
                    car.fleet = fleets;
                    fleets++;
                    currentMaxTime = car.time;
                    document.getElementById('statusMessage').textContent =
                        `Car at position ${car.position}: time=${car.time.toFixed(2)} > maxTime=${(currentMaxTime === car.time ? 0 : currentMaxTime).toFixed(2)} → NEW FLEET #${fleets}!`;
                } else {
                    // Joins previous fleet
                    car.fleet = fleets - 1;
                    document.getElementById('statusMessage').textContent =
                        `Car at position ${car.position}: time=${car.time.toFixed(2)} ≤ maxTime=${currentMaxTime.toFixed(2)} → Catches up & joins Fleet #${fleets}`;
                }

                document.getElementById('maxTimeVal').textContent = currentMaxTime.toFixed(2);
                document.getElementById('fleetVal').textContent = fleets;

                drawRoad();
                renderCarsTable();

                currentCarIndex++;
            }
        }

        function toggleAuto() {
            if (autoInterval) {
                stopAuto();
            } else {
                document.getElementById('autoBtn').textContent = 'Pause';
                autoInterval = setInterval(() => {
                    if (phase === 'done') {
                        stopAuto();
                    } else {
                        step();
                    }
                }, 1500);
            }
        }

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

        function reset() {
            stopAuto();
            phase = 'init';
            document.getElementById('stepBtn').disabled = false;
            document.getElementById('statusMessage').textContent =
                'Click "Step" or "Auto Run" to see how cars form fleets';
            init();
        }

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