1
Just Enough Ones
code-golf sequence combinatorics binary-matrix
Challenge
Given a positive integer \$n\$, count the number of \$n\times n\$ binary matrices (i.e. whose entries are \$0\$ or \$1\$) with exactly two \$1\$'s in each rows and two \$1\$'s in each column.
Here are a few examples of vali...