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45 lines
2.8 KiB
HTML
45 lines
2.8 KiB
HTML
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<p>Along a long library corridor, there is a line of seats and decorative plants. You are given a <strong>0-indexed</strong> string <code>corridor</code> of length <code>n</code> consisting of letters <code>'S'</code> and <code>'P'</code> where each <code>'S'</code> represents a seat and each <code>'P'</code> represents a plant.</p>
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<p>One room divider has <strong>already</strong> been installed to the left of index <code>0</code>, and <strong>another</strong> to the right of index <code>n - 1</code>. Additional room dividers can be installed. For each position between indices <code>i - 1</code> and <code>i</code> (<code>1 <= i <= n - 1</code>), at most one divider can be installed.</p>
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<p>Divide the corridor into non-overlapping sections, where each section has <strong>exactly two seats</strong> with any number of plants. There may be multiple ways to perform the division. Two ways are <strong>different</strong> if there is a position with a room divider installed in the first way but not in the second way.</p>
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<p>Return <em>the number of ways to divide the corridor</em>. Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>. If there is no way, return <code>0</code>.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/12/04/1.png" style="width: 410px; height: 199px;" />
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<pre>
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<strong>Input:</strong> corridor = "SSPPSPS"
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<strong>Output:</strong> 3
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<strong>Explanation:</strong> There are 3 different ways to divide the corridor.
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The black bars in the above image indicate the two room dividers already installed.
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Note that in each of the ways, <strong>each</strong> section has exactly <strong>two</strong> seats.
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</pre>
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<p><strong>Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/12/04/2.png" style="width: 357px; height: 68px;" />
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<pre>
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<strong>Input:</strong> corridor = "PPSPSP"
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> There is only 1 way to divide the corridor, by not installing any additional dividers.
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Installing any would create some section that does not have exactly two seats.
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</pre>
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<p><strong>Example 3:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/12/12/3.png" style="width: 115px; height: 68px;" />
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<pre>
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<strong>Input:</strong> corridor = "S"
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> There is no way to divide the corridor because there will always be a section that does not have exactly two seats.
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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>n == corridor.length</code></li>
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<li><code>1 <= n <= 10<sup>5</sup></code></li>
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<li><code>corridor[i]</code> is either <code>'S'</code> or <code>'P'</code>.</li>
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</ul>
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