LeetCode - 646 - Maximum Length of Pair Chain

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概述

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]

Note:

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

给你一个pair对数组，若存在(a, b) (c, d) && b < c 那么就能构成一条链，求最长的链的长度

排序，遍历。时间复杂度O(nlgn)，空间复杂度O(1)

class Solution {
public:
    int findLongestChain(vector<vector<int>>& pairs) {
        if (pairs.empty()) return 0;
        sort(pairs.begin(), pairs.end(), cmp);
        int cnt = 0;
        int pre = INT_MIN;
        for (int i = 0; i < pairs.size(); ++i) {
            if (pairs[i][0] > pre) {
                cnt++;
                pre = pairs[i][1];
            }
        }
        return cnt;
    }
    
    static bool cmp(vector<int> a, vector<int> b) {
        if (a[1] == b[1])
            return a[0] < b[0];
        return a[1] < b[1];
    }
};