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38 lines
1.7 KiB
HTML
38 lines
1.7 KiB
HTML
<p>You are given an array <code>routes</code> representing bus routes where <code>routes[i]</code> is a bus route that the <code>i<sup>th</sup></code> bus repeats forever.</p>
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<ul>
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<li>For example, if <code>routes[0] = [1, 5, 7]</code>, this means that the <code>0<sup>th</sup></code> bus travels in the sequence <code>1 -> 5 -> 7 -> 1 -> 5 -> 7 -> 1 -> ...</code> forever.</li>
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</ul>
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<p>You will start at the bus stop <code>source</code> (You are not on any bus initially), and you want to go to the bus stop <code>target</code>. You can travel between bus stops by buses only.</p>
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<p>Return <em>the least number of buses you must take to travel from </em><code>source</code><em> to </em><code>target</code>. Return <code>-1</code> if it is not possible.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> routes = [[1,2,7],[3,6,7]], source = 1, target = 6
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The best strategy is take the first bus to the bus stop 7, then take the second bus to the bus stop 6.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12
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<strong>Output:</strong> -1
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= routes.length <= 500</code>.</li>
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<li><code>1 <= routes[i].length <= 10<sup>5</sup></code></li>
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<li>All the values of <code>routes[i]</code> are <strong>unique</strong>.</li>
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<li><code>sum(routes[i].length) <= 10<sup>5</sup></code></li>
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<li><code>0 <= routes[i][j] < 10<sup>6</sup></code></li>
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<li><code>0 <= source, target < 10<sup>6</sup></code></li>
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</ul>
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