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54 lines
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54 lines
3.1 KiB
HTML
<p>There is a <strong>3 lane road</strong> of length <code>n</code> that consists of <code>n + 1</code> <strong>points</strong> labeled from <code>0</code> to <code>n</code>. A frog <strong>starts</strong> at point <code>0</code> in the <strong>second </strong>lane<strong> </strong>and wants to jump to point <code>n</code>. However, there could be obstacles along the way.</p>
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<p>You are given an array <code>obstacles</code> of length <code>n + 1</code> where each <code>obstacles[i]</code> (<strong>ranging from 0 to 3</strong>) describes an obstacle on the lane <code>obstacles[i]</code> at point <code>i</code>. If <code>obstacles[i] == 0</code>, there are no obstacles at point <code>i</code>. There will be <strong>at most one</strong> obstacle in the 3 lanes at each point.</p>
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<ul>
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<li>For example, if <code>obstacles[2] == 1</code>, then there is an obstacle on lane 1 at point 2.</li>
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</ul>
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<p>The frog can only travel from point <code>i</code> to point <code>i + 1</code> on the same lane if there is not an obstacle on the lane at point <code>i + 1</code>. To avoid obstacles, the frog can also perform a <strong>side jump</strong> to jump to <strong>another</strong> lane (even if they are not adjacent) at the <strong>same</strong> point if there is no obstacle on the new lane.</p>
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<ul>
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<li>For example, the frog can jump from lane 3 at point 3 to lane 1 at point 3.</li>
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</ul>
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<p>Return<em> the <strong>minimum number of side jumps</strong> the frog needs to reach <strong>any lane</strong> at point n starting from lane <code>2</code> at point 0.</em></p>
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<p><strong>Note:</strong> There will be no obstacles on points <code>0</code> and <code>n</code>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/03/25/ic234-q3-ex1.png" style="width: 500px; height: 244px;" />
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<pre>
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<strong>Input:</strong> obstacles = [0,1,2,3,0]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The optimal solution is shown by the arrows above. There are 2 side jumps (red arrows).
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Note that the frog can jump over obstacles only when making side jumps (as shown at point 2).
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/03/25/ic234-q3-ex2.png" style="width: 500px; height: 196px;" />
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<pre>
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<strong>Input:</strong> obstacles = [0,1,1,3,3,0]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> There are no obstacles on lane 2. No side jumps are required.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/03/25/ic234-q3-ex3.png" style="width: 500px; height: 196px;" />
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<pre>
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<strong>Input:</strong> obstacles = [0,2,1,0,3,0]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> The optimal solution is shown by the arrows above. There are 2 side jumps.
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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>obstacles.length == n + 1</code></li>
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<li><code>1 <= n <= 5 * 10<sup>5</sup></code></li>
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<li><code>0 <= obstacles[i] <= 3</code></li>
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<li><code>obstacles[0] == obstacles[n] == 0</code></li>
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</ul>
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