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

Note:

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

分析

按照第二个元素的大小对pairs进行排序。最长链是以第一个pair开始的，遍历，记录下每次”follow“的pair的第二个元素为pre，计数。

code

#include <iostream>#include<algorithm>#include<vector> using namespace std;class Solution {public:    int findLongestChain(vector<vector<int> >& pairs) {        sort(pairs.begin(),pairs.end(),compare);        int count=0, pre;        for (int i = 0; i < pairs.size(); ++i) {            if(i==0) {                count++;                pre=pairs[i][1];            }        if (pairs[i][0] > pre) {        count++;        pre=pairs[i][1];        }        }        return count;    }    static bool compare(vector<int> a, vector<int> b) {if (a[1]==b[1])return a[0] < b[0];else return a[1]<b[1];}};