Counting Valid 2x2 Submatrices and Optimizing Zero-Prefix Products
To solve this problem, we scan every possible 2x2 submatrix in a n × m grid and check whether the four characters within it collectively contain at least one 'y', one 'o', and one 'u'. The order does not matter—only the presence of all three required characters.
The algorithm iterates over all valid top-left corners of 2x2 blocks (from row 1 to ...
Posted on Wed, 24 Jun 2026 17:58:58 +0000 by webdes03