solve: nonOverlappingIntervals

Author: yolophg

non-overlapping-intervals/yolophg.py

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+# Time Complexity: O(N log N) 
+# (1) sorting the intervals takes O(N log N), and 
+# (2) iterating through them takes O(N).
+# (3) so the overall complexity is O(N log N).
+# Space Complexity: O(1) - only use a few extra variables (end and res), so the space usage is constant.
+
+class Solution:
+    def eraseOverlapIntervals(self, intervals: List[List[int]]) -> int:
+        # sort intervals by their ending time
+        intervals.sort(key=lambda x: x[1])  
+        
+        # track the last non-overlapping interval's end
+        end = float('-inf') 
+        # count the number of intervals we need to remove
+        res = 0  
+
+        for interval in intervals:
+            # if it overlaps with the last interval
+            if interval[0] < end: 
+                # need to remove this one 
+                res += 1  
+            else:
+                # otherwise, update the end to the current interval's end
+                end = interval[1] 
+        return res