source: https://leetcode.com/problems/maximum-length-of-pair-chain/description/ Maximum Length of Pair Chain You are given an array of n pairs pairs where pairs[i] = [lefti, righti] and lefti < righti. A pair p2 = [c, d] follows a pair p1 = [a, b] if b < c. A chain of pairs can be formed in this fashion. Return the length ...