17.3 find_minimum_visits

17-greedy/find_minimum_visits.py

@@ -0,0 +1,44 @@
+# O(nlogn) time, O(1) space
+def find_minimum_visits(intervals):
+    # [0, 3]
+    # [2, 6] -> [2, 3]
+    # [3, 4] -> 3
+    # [6, 9] -> 6
+    intervals.sort(key=lambda interval: interval[0])
+    current = []
+    res = []
+
+    for interval in intervals:
+        if not current:
+            current = interval
+            continue
+        current = [max(current[0], interval[0]), min(current[1], interval[1])]
+        if current[0] == current[1]:
+            res.append(current[0])
+            current = []
+
+    if current:
+        res.append(current[0])
+
+    return res
+
+
+# O(nlogn) time, O(1) space
+def find_minimum_visits_2(intervals):
+    # sort intervals by endpoints
+    intervals.sort(key=lambda interval: interval[1])
+    # [0, 3], [3, 4], [2, 6], [6, 9]
+    last_visit_time = float("-inf")
+    res = []
+    for interval in intervals:
+        if interval[0] > last_visit_time:
+            last_visit_time = interval[1]
+            res.append(last_visit_time)
+    return res
+
+
+if __name__ == "__main__":
+    intervals = [[0, 3], [2, 6], [3, 4], [6, 9]]
+    assert find_minimum_visits(intervals) == [3, 6]
+    assert find_minimum_visits_2(intervals) == [3, 9]
+    print("All tests passed!")

README.md

@@ -109,7 +109,7 @@
     - [x] Boot-camp 03/16
     - [x] 17.1 Compute an Optimum Assignment of Tasks 03/16
     - [x] 17.2 Schedule to Minimize Waiting Time 03/17
-    - [ ] 17.3 The Interval Covering Problem
+    - [x] 17.3 The Interval Covering Problem 03/18
     - ...
 
 # LeetCode