Add problem 97 - Interleaving String

Author: anirudhology

problems/dynamic_programming/interleaving_string.py

@@ -0,0 +1,25 @@
+class InterleavingString:
+    def isInterleave(self, s1: str, s2: str, s3: str) -> bool:
+        # Lengths of the strings
+        m, n = len(s1), len(s2)
+        # Special case
+        if m + n != len(s3):
+            return False
+        # Lookup table to store if s3[0...k] can be formed by s1[0...i] and
+        # s2[0...j]
+        lookup = [[False] * (n + 1) for _ in range(m + 1)]
+        # For empty strings
+        lookup[0][0] = True
+        # If s2 is empty
+        for i in range(1, m + 1):
+            lookup[i][0] = lookup[i - 1][0] and s1[i - 1] == s3[i - 1]
+        # If s1 is empty
+        for j in range(1, n + 1):
+            lookup[0][j] = lookup[0][j - 1] and s2[j - 1] == s3[j - 1]
+        # Populate the remaining table
+        for i in range(1, m + 1):
+            for j in range(1, n + 1):
+                lookup[i][j] = (lookup[i - 1][j] and s1[i - 1] == s3[i + j - 1]) or (
+                            lookup[i][j - 1] and s2[j - 1] == s3[i + j - 1])
+
+        return lookup[m][n]

tests/dynamic_programming/interleaving_string_test.py

@@ -0,0 +1,26 @@
+import unittest
+
+from problems.dynamic_programming.interleaving_string import InterleavingString
+
+
+class TestInterleavingString(unittest.TestCase):
+
+    def setUp(self):
+        self.interleaving_string = InterleavingString()
+
+    def test_interleave(self):
+        self.assertTrue(self.interleaving_string.isInterleave("aabcc", "dbbca", "aadbbcbcac"))
+        self.assertFalse(self.interleaving_string.isInterleave("aabcc", "dbbca", "aadbbbaccc"))
+        self.assertTrue(self.interleaving_string.isInterleave("", "", ""))
+        self.assertTrue(self.interleaving_string.isInterleave("a", "", "a"))
+        self.assertTrue(self.interleaving_string.isInterleave("", "b", "b"))
+        self.assertFalse(self.interleaving_string.isInterleave("abc", "def", "abdccfe"))
+
+    def test_edge_cases(self):
+        self.assertFalse(self.interleaving_string.isInterleave("abc", "def", "abcdefg"))
+        self.assertTrue(self.interleaving_string.isInterleave("abc", "def", "adbcef"))
+        self.assertFalse(self.interleaving_string.isInterleave("", "a", "b"))
+
+
+if __name__ == '__main__':
+    unittest.main()