solve Insert Interval

Author: saubhik

problems/insert_interval.py

@@ -0,0 +1,50 @@
+from typing import List
+
+
+class Solution:
+    # Greedy.
+    # The idea of greedy algorithm is to pick the locally optimal move at each step,
+    # that will lead to the globally optimal solution.
+    #
+    # newInterval can be:
+    # - ends before start of current interval
+    # - ends between start and end of current interval
+    # - starts between start and end of current interval
+    # - starts after end of current interval
+    #
+    # Time: O(n)
+    # Space: O(n) to keep output.
+    def insert(
+        self, intervals: List[List[int]], newInterval: List[int]
+    ) -> List[List[int]]:
+        merged = False
+        ans = []
+
+        for interval in intervals:
+            if merged:
+                ans.append(interval)
+
+            # ends before start of current interval
+            elif newInterval[1] < interval[0]:
+                ans.append(newInterval)
+                ans.append(interval)
+                merged = True
+
+            # ends between start and end of current interval
+            elif interval[0] <= newInterval[1] <= interval[1]:
+                interval[0] = min(interval[0], newInterval[0])
+                ans.append(interval)
+                merged = True
+
+            # starts between start and end of current interval
+            elif interval[0] <= newInterval[0] <= interval[1]:
+                newInterval = [interval[0], max(newInterval[1], interval[1])]
+
+            # starts after end of current interval
+            elif interval[1] < newInterval[0]:
+                ans.append(interval)
+
+        if not merged:
+            ans.append(newInterval)
+
+        return ans

tests/test_insert_interval.py

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+import unittest
+
+from insert_interval import Solution
+
+
+class TestInsertInterval(unittest.TestCase):
+    def test_example_1(self):
+        assert Solution().insert(intervals=[[1, 3], [6, 9]], newInterval=[2, 5]) == [
+            [1, 5],
+            [6, 9],
+        ]
+
+    def test_example_2(self):
+        assert Solution().insert(
+            intervals=[[1, 2], [3, 5], [6, 7], [8, 10], [12, 16]], newInterval=[4, 8]
+        ) == [[1, 2], [3, 10], [12, 16]]