646. Maximum Length of Pair Chain

Problem:

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].

思路：

Solution (C++):

int findLongestChain(vector<vector<int>>& pairs) {
    if (pairs.empty() || pairs[0].empty())  return 0;
    sort(pairs.begin(), pairs.end(), cmp);
    int count = 1;     
    vector<int> tmp = pairs[0];

    for (int i = 1; i < pairs.size(); ++i) {
        if (pairs[i][0] > tmp[1]) {
            tmp = pairs[i];
            ++count;
        }
    }
    return count;
}
static bool cmp(vector<int>& a, vector<int>& b) {
    return a[1] < b[1];
}

性能：

Runtime: 80 ms  Memory Usage: 15.1 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB