Microsoft Interview: transforming a matrix

Question

Given a matrix of size n x m filled with 0\'s and 1\'s

e.g.:

1 1 0 1 0

0 0 0 0 0

0 1 0 0 0

1 0 1 1 0

if the matrix has 1 a

Answer 1

Another solution would be to scan the matrix as usual, and at the first 1 you split the matrix in 4 quadrants. You then set the line and the column to 1's, and recursively process each quadrant. Just make sure to set the whole columns and rows, even though you are scanning only a quadrant.