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Count the number of unique paths from (0,0) to (m-1,n-1) on an m×n binary grid where moves are only right or down, but attempting to enter a mirror cell redirects the robot perpendicularly (right→down, down→right) and can chain until a non-mirror or out-of-bounds (which makes the path invalid). The core challenge is counting direction-aware transitions (with possible repeated reflections) efficiently and returning the total modulo 1e9+7.
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Leetcode 3665. Twisted Mirror Path Count
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Source snapshot: Nov 12, 2026
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