Leetcode Problem 1359. Count All Valid Pickup and Delivery Options

1359. Count All Valid Pickup and Delivery Options

Leetcode Solutions

Permutations (Math)

  1. Initialize MOD as 10^9 + 7 to prevent integer overflow.
  2. Initialize total to 1, which will hold the final count of valid sequences.
  3. Loop from 1 to n, and for each i, multiply total by i to account for the number of ways to arrange the pickups.
  4. For each i, also multiply total by (2 * i - 1) to account for the number of valid places to insert the corresponding delivery.
  5. After the loop, return total modulo MOD.
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Recursion with Memoization (Top-Down DP)

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