matrix_convert_to_zero by Jessie

[jessiezhang2017]

if the matrix has m columns and n rows , the space complexity is O(n+m)
time complexity is O(n*m)

[shrutivanw]

Nice work!

The only further optimization I could think of was to use the 0th row and the 0th column to track which columns and rows need to be converted to zero. Here's my solution with that: https://github.com/Ada-C10/matrix_convert_to_zero/blob/solution-basic/lib/matrix_convert_to_zero.rb