Rooks

Arya has a chessboard with $N$ rows (numbered $1$ through $N$) and $N$ columns (numbered $1$ through $N$); a square in row $r$ and column $c$ is denoted by $(r, c)$. Arya has already placed $K$ rooks on the chessboard in such a way that no two rooks attack each other. Note that two rooks attack each other if they are in the same row or in the same column and there is no rook between them. She is