Leetcode 646. Maximum Length of Pair Chain 找最长链 解题报告

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这道题么，找最长的链，所谓的链就是上一个的结尾一定大于下一个的开头

因为要找最长的链，所以我们按照结尾的那个数字排序，这样可以尽量的最长
然后从第一个开始，直接往后遍历找就好，反正在前面的一定是一个最优解（因为不要求区间覆盖的覆盖长度，而是要求pair的数量）

相对的，如果是要找区间最长，应该就是排序后要上DP了，而不是这样直接找

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

public class Solution {
   public int findLongestChain(int[][] pairs) {
       //sort
       /**
       按照截止排序，就可以找到最优的组合方案了
       **/
       Arrays.sort(pairs, (a,b) -> a[1] - b[1]);
       int sum = 0, n = pairs.length;
       int i = 0;
       while (i < n){
           int current_end = pairs[i][1];
           sum ++;
           while ( i < n && pairs[i][0] <= current_end) i++;
       }
       return sum;

    }
}