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

Note:

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

public class Solution {
    // Greedy -> O(NlogN)
    // Consider pairs as jobs, with [start time, end time],
    // Then the problem is converted to ask the maximum jobs we can accomplish.
    public int findLongestChain(int[][] pairs) {
        if (pairs == null || pairs.length == 0)
            return 0;
        Arrays.sort(pairs, (a, b) -> (a[1] - b[1]));
        int res = 1, end = pairs[0][1];
        for (int i = 1; i < pairs.length; i++) {
            if (pairs[i][0] > end) {
                res++;
                end = pairs[i][1];
            }
        }
        return res;
    }
}