Add solution for "Truncate Sentence" with unit tests.

problems/easy/truncate_sentence_1816/solution.py

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+# Tags: String
+
+
+class Solution:
+    def truncate_sentence(self, s: str, k: int) -> str:
+        """
+        Time complexity: O(n)
+        Breakdown:
+        - s.split(): Splits the string into a list of words - O(n) where n is the length of the string
+        - [:k]: Slices the first k elements from the list - O(k) where k is the number of words to keep
+        - ' '.join(): Joins k words back into a string - O(n) to construct the result string
+        Since k <= n (the number of words cannot exceed the string length), overall time complexity is O(n)
+
+        Space complexity: O(n)
+        Breakdown:
+        - The split() operation creates a list of all words in the string - O(n) space
+        - The join() operation creates a new string for the result - O(n) space
+        Overall: O(n) additional space
+        """
+        return ' '.join(s.split()[:k])

problems/easy/truncate_sentence_1816/test_solution.py

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+import pytest
+from tests.base_test import BaseTestSolution
+from .solution import Solution
+
+
+class TestSolution(BaseTestSolution):
+    solution = Solution()
+
+    @pytest.mark.parametrize("method_name, s, k, expected, timeout", [
+        ('truncate_sentence', "Hello how are you Contestant", 4, "Hello how are you", None),
+        ('truncate_sentence', "What is the solution to this problem", 4, "What is the solution", None),
+        ('truncate_sentence', "chopper is not a tanuki", 5, "chopper is not a tanuki", None),
+    ])
+    def test_truncate_sentence(self, method_name, s, k, expected, timeout):
+        self._run_test(self.solution, method_name, (s, k,), expected, timeout)