Longest chain of pairs

Question

You are given n pairs of numbers. In every pair, the first number is always smaller than the second number. A pair (c,d) can follow

Answer 1

We can start with Brian's approach, of sorting all the pairs based on y value. It will ensure the required condition of prev pair's X < next pair's y. Now all we need is longest increasing subsequence of x among the new list of pairs. Which we can get by sorting all x and finding longest common subsequence between sorted x and new list previously created