354. 俄罗斯套娃信封问题

class Solution {
public:
    int maxEnvelopes(vector<vector<int>>& envelopes) {
        if (envelopes.empty()) {
            return 0;
        }

        sort(envelopes.begin(), envelopes.end(), [](auto e1, auto e2) 
        {
            return e1[0] < e2[0] || (e1[0] == e2[0] && e1[1] > e2[1]);
        });
        int n = envelopes.size();
        
        vector<int> f(n, 1);
        for (int i = 1; i < n; ++i) 
        {
            for (int j = 0; j < i; ++j) 
            {
                if (envelopes[j][1] < envelopes[i][1])
                {
                    f[i] = max(f[i], f[j] + 1);
                }
            }
        }
        return *max_element(f.begin(), f.end());
    }
};