759.cpp

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class Solution {
public:
    vector<Interval> employeeFreeTime(vector<vector<Interval>>& schedule) {
        vector<Interval> res, v;
        for (auto a : schedule) {
            v.insert(v.end(), a.begin(), a.end());
        }
        sort(v.begin(), v.end(), [](Interval &a, Interval &b) {return a.start < b.start;});
        Interval t = v[0];
        for (Interval i : v) {
            if (t.end < i.start) {
                res.push_back(Interval(t.end, i.start));
                t = i;
            } else {
                t = (t.end < i.end) ? i : t;
            }
        }
        return res;
    }
};
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class Solution {
public:
    vector<Interval> employeeFreeTime(vector<vector<Interval>>& schedule) {
        vector<Interval> res;
        map<int, int> m;
        int cnt = 0;
        for (auto employee : schedule) {
            for (Interval i : employee) {
                ++m[i.start];
                --m[i.end];
            }
        }
        for (auto a : m) {
            cnt += a.second;
            if (!cnt) res.push_back(Interval(a.first, 0));
            if (cnt && !res.empty() && !res.back().end) res.back().end = a.first;
        }
        if (!res.empty()) res.pop_back();
        return res;
    }
};
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