Status: IN
A cell is special iff `mat[i][j] == 1`, `row_sums[i] == 1`, and `col_sums[j] == 1`; the `mat[i][j] == 1` check is technically redundant but short-circuits the sum lookups for the majority-zero cells.
Source: entries/2026/06/06/special-positions-in-a-binary-matrix-solution.md