646.Maximum Length of Pair Chain

646.Maximum Length of Pair Chain

• 题目描述：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]

• 题目大意：给定一组pair，找到最长的pair链

• 思路：DP，dp[i]表示到当前pair最长的链（chain）

• 代码

  package DP;
  
  import java.util.Arrays;
  import java.util.Comparator;
  
  /**
  * @Author OovEver
  * @Date 2017/12/17 16:41
  */
  public class LeetCode646 {
    public static int findLongestChain(int[][] pairs) {
        Arrays.sort(pairs, new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o1[0]-o2[0];
            }
        });
        int[] dp = new int[pairs.length];
        Arrays.fill(dp, 1);
        for(int i=0;i<pairs.length;i++) {
            for(int j=0;j<i;j++) {
                dp[i] = Math.max(pairs[i][0] > pairs[j][1] ? dp[j] + 1 : dp[j], dp[i]);
            }
        }
        return dp[pairs.length-1];
    }
  
  
  }