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class Solution {
public:
    int maxEnvelopes(vector<vector<int>>& envelopes) {
        // Sort the envelopes.
        sort(envelopes.begin(), envelopes.end(), [](auto &a, auto &b){return a[0]<b[0] || (a[0] == b[0] && a[1] > b[1]);});

        // Find lis of height.
        vector<int> seq;
        for(auto &env: envelopes){
            auto it = lower_bound(seq.begin(), seq.end(), env[1]);
            if(it == seq.end())
                seq.push_back(env[1]);
            else
                seq[it-seq.begin()] = env[1];
        }
        return seq.size();
    }
};