Algorithm/DS Problem#3: Minimum non-overlapping bridges

You are given n coordinates[north, south] of N bridges
Count of maximum number of non-overlapping bridges.

Ex: [[6,2],[4,3],[2,6],[1,5]]
    6 4 2 1 North
    2 3 6 5 South
    B1 B2 B3 B4
Output: 2

For non-overlapping bridges, the following is TRUE:
     north1 < north2 and South1 < South2
     1      <   2    and 2     <     6
Idea here is to do the below:
 (a) Sort all bridges based on north bank
 (b) Find the LIS(Longest Increasing Subsequence) for each bridge based on south bank