DE shaw latest questions

Given a 2-D matrix consisting of n rows and m columns. Find the length of the longest non-decreasing sequence by taking at most one element from each column without changing the order of the columns.  Note: the order of choosing columns should be strictly increasing  Ex: given n=3 m=4 2 6 3 5 8 9 4 6 5 8 9 7 possible answers are : { 2,6,9}, { 2,8,9} , { 5,6,9} , { 5,8,9} , { 2, 3,5 } ...