Maximum Length of Pair Chain

题目地址：
https://leetcode.com/problems/maximum-length-of-pair-chain/description/

题目：

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

解题思路：
这道题就是用动态规划来解决。

代码：

public int findLongestChain(int[][] pairs) {
    if (pairs == null || pairs.length == 0) return 0;
    Arrays.sort(pairs, (a, b) -> (a[0] - b[0]));
    int[] dp = new int[pairs.length];
    Arrays.fill(dp, 1);
    for (int i = 0; i < dp.length; i++) {
        for (int j = 0; j < i; j++) {
            dp[i] = Math.max(dp[i], pairs[i][0] > pairs[j][1]? dp[j] + 1 : dp[j]);
        }
    }
    return dp[pairs.length - 1];
}