Create employee-free-time.cpp

Author: kamyu104

C++/employee-free-time.cpp

@@ -0,0 +1,37 @@
+// Time:  O(m * logn), m is the number of schedule, n is the number of employees, m >= n
+// Space: O(n)
+
+/**
+ * Definition for an interval.
+ * struct Interval {
+ *     int start;
+ *     int end;
+ *     Interval() : start(0), end(0) {}
+ *     Interval(int s, int e) : start(s), end(e) {}
+ * };
+ */
+class Solution {
+public:
+    vector<Interval> employeeFreeTime(vector<vector<Interval>>& schedule) {
+        vector<Interval> result;
+        using P = pair<int, pair<int, int>>;
+        priority_queue<P, vector<P>, greater<P>> min_heap;
+        for (int i = 0; i < schedule.size(); ++i) {
+            min_heap.emplace(schedule[i][0].start, make_pair(i, 0));
+        }
+        int last_end = -1;
+        while (!min_heap.empty()) {
+            int t;
+            pair<int, int> p;
+            tie(t, p) = min_heap.top(); min_heap.pop();
+            if (0 <= last_end && last_end < t) {
+                result.emplace_back(last_end, t);
+            }
+            last_end = max(last_end, schedule[p.first][p.second].end);
+            if (p.second + 1 < schedule[p.first].size()) {
+                min_heap.emplace(schedule[p.first][p.second + 1].start, make_pair(p.first, p.second + 1));
+            }
+        }
+        return result;
+    }
+};