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

Note:

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

Analysis:
This problem is actually a LIS question.

Code (Java):

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class Solution {     public int findLongestChain(int[][] pairs) {         if (pairs == null || pairs.length == 0) {             return 0;         }                   Arrays.sort(pairs, new PairComparator());                   int ans = 1;         int[] dp = new int[pairs.length];                   for (int i = 0; i < pairs.length; i++) {             dp[i] = 1;             for (int j = 0; j < i; j++) {                 if (pairs[i][0] > pairs[j][1]) {                     dp[i] = Math.max(dp[i], dp[j] + 1);                 }             }                           ans = Math.max(ans, dp[i]);         }                   return ans;     } }   class PairComparator implements Comparator<int[]> {     @Override     public int compare(int[] a, int[] b) {         if (a[0] != b[0]) {             return a[0] - b[0];         }           return a[1] - b[1];     } }