Add problem 115 - Distinct Subsequences

Author: anirudhology

problems/dynamic_programming/distinct_subsequences.py

@@ -0,0 +1,20 @@
+class DistinctSubsequences:
+    @staticmethod
+    def numDistinct(s: str, t: str) -> int:
+        # Lengths of both strings
+        m, n = len(s), len(t)
+        # Lookup table to store count of distinct subsequences
+        lookup = [[0 for j in range(n + 1)] for i in range(m + 1)]
+        # If t is empty, it can be subsequence of every string but only once
+        for i in range(m + 1):
+            lookup[i][0] = 1
+        # If both strings are empty
+        lookup[0][0] = 1
+        # Populate the remaining table
+        for j in range(1, n + 1):
+            for i in range(1, m + 1):
+                lookup[i][j] = lookup[i - 1][j]
+                # If characters are same
+                if s[i - 1] == t[j - 1]:
+                    lookup[i][j] += lookup[i - 1][j - 1]
+        return lookup[m][n]

tests/dynamic_programming/distinct_subsequences_test.py

@@ -0,0 +1,30 @@
+import unittest
+
+from problems.dynamic_programming.distinct_subsequences import DistinctSubsequences
+
+
+class TestDistinctSubsequences(unittest.TestCase):
+
+    def setUp(self):
+        self.distinct_subsequences = DistinctSubsequences()
+
+    def test_num_distinct_empty_strings(self):
+        self.assertEqual(self.distinct_subsequences.numDistinct("", ""), 1)
+
+    def test_num_distinct_empty_target(self):
+        self.assertEqual(self.distinct_subsequences.numDistinct("abc", ""), 1)
+
+    def test_num_distinct_empty_source(self):
+        self.assertEqual(self.distinct_subsequences.numDistinct("", "abc"), 0)
+
+    def test_num_distinct_same_strings(self):
+        self.assertEqual(self.distinct_subsequences.numDistinct("abc", "abc"), 1)
+
+    def test_num_distinct_general_cases(self):
+        self.assertEqual(self.distinct_subsequences.numDistinct("babgbag", "bag"), 5)
+        self.assertEqual(self.distinct_subsequences.numDistinct("rabbbit", "rabbit"), 3)
+        self.assertEqual(self.distinct_subsequences.numDistinct("abc", "def"), 0)
+
+
+if __name__ == "__main__":
+    unittest.main()