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39 lines
1.0 KiB
HTML
39 lines
1.0 KiB
HTML
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<p>Given <code>n</code> orders, each order consist in pickup and delivery services. </p>
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<p>Count all valid pickup/delivery possible sequences such that delivery(i) is always after of pickup(i). </p>
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<p>Since the answer may be too large, return it modulo 10^9 + 7.</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> n = 1
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> Unique order (P1, D1), Delivery 1 always is after of Pickup 1.
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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> n = 2
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<strong>Output:</strong> 6
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<strong>Explanation:</strong> All possible orders:
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(P1,P2,D1,D2), (P1,P2,D2,D1), (P1,D1,P2,D2), (P2,P1,D1,D2), (P2,P1,D2,D1) and (P2,D2,P1,D1).
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This is an invalid order (P1,D2,P2,D1) because Pickup 2 is after of Delivery 2.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> n = 3
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<strong>Output:</strong> 90
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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 <= n <= 500</code></li>
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</ul>
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