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].

Runtime: 48 ms, faster than 63.85% of C++ online submissions for Maximum Length of Pair Chain.

排序然後two pointer。爭取一次AC。

class Solution {
public:
  static bool cmp(const vector<int>& a, const vector<int>& b){
    return a[1] < b[1];
  }
  int findLongestChain(vector<vector<int>>& pairs) {
    sort(pairs.begin(),pairs.end(),cmp);
    int ret = 0, i = 0,j = 1
 
;
    while(j < pairs.size()){
      if(pairs[i][1] < pairs[j][0]){
        ret++;
        i = j;
        j++;
      }else j++;
    }
    return ret+1;
  }
};