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LeetCode

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Problem

You have two types of tiles: a 2 x 1 domino shape and a tromino shape. You may rotate these shapes.

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Given an integer n, return the number of ways to tile an 2 x n board. Since the answer may be very large, return it modulo $10^9 + 7$.

In a tiling, every square must be covered by a tile. Two tilings are different if and only if there are two 4-directionally adjacent cells on the board such that exactly one of the tilings has both squares occupied by a tile.

Example 1:

img

Input: n = 3
Output: 5
Explanation: The five different ways are show above.

Example 2:

Input: n = 1
Output: 1

Constraints:

  • 1 <= n <= 1000

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