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 longest chain which can be formed.
\n\nYou do not need to use up all the given intervals. You can select pairs in any order.
\n\n\n
Example 1:
\n\n\nInput: pairs = [[1,2],[2,3],[3,4]]\nOutput: 2\nExplanation: The longest chain is [1,2] -> [3,4].\n\n\n
Example 2:
\n\n\nInput: pairs = [[1,2],[7,8],[4,5]]\nOutput: 3\nExplanation: The longest chain is [1,2] -> [4,5] -> [7,8].\n\n\n
\n
Constraints:
\n\nn == pairs.length1 <= n <= 1000-1000 <= lefti < righti <= 1000给你一个由 n 个数对组成的数对数组 pairs ，其中 pairs[i] = [lefti, righti] 且 lefti < righti 。
现在，我们定义一种 跟随 关系，当且仅当 b < c 时，数对 p2 = [c, d] 才可以跟在 p1 = [a, b] 后面。我们用这种形式来构造 数对链 。
找出并返回能够形成的 最长数对链的长度 。
\n\n你不需要用到所有的数对，你可以以任何顺序选择其中的一些数对来构造。
\n\n\n\n
示例 1：
\n\n\n输入：pairs = [[1,2], [2,3], [3,4]]\n输出：2\n解释：最长的数对链是 [1,2] -> [3,4] 。\n\n\n
示例 2：
\n\n\n输入：pairs = [[1,2],[7,8],[4,5]]\n输出：3\n解释：最长的数对链是 [1,2] -> [4,5] -> [7,8] 。\n\n
\n\n
提示：
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