[LeetCode]Maximum Length of Pair Chain

题目描述：

LeetCode 646. Maximum Length of Pair Chain

You are given n pairs of numbers. In every pair, the first number is always smaller than the second number.

Now, we define a pair (c, d) can follow another pair (a, b) if and only if b < c. Chain of pairs can be formed in this fashion.

Given a set of pairs, find the length longest chain which can be formed. You needn't use up all the given pairs. You can select pairs in any order.

Example 1:

Input: [[1,2], [2,3], [3,4]]Output: 2Explanation: The longest chain is [1,2] -> [3,4]

Note:

1. The number of given pairs will be in the range [1, 1000].

题目大意：

给定一组数对，我们定义当且仅当b < c时，(c, d)可以链在(a, b)之后。求可以组成的最长数对链的长度。

解题思路：

数对根据第二个元素进行排序，一趟遍历。

Python代码：

class Solution(object):
    def findLongestChain(self, pairs):
        """
        :type pairs: List[List[int]]
        :rtype: int
        """
        pairs.sort(key = lambda x: x[1])
        last = [-0x7FFFFFFF, -0x7FFFFFFF]
        ans = 0
        for p in pairs:
            if p[0] > last[1]:
                ans += 1
                last = p
        return ans