Create DecodedStringAtIndex.py

Author: DreamOfTheRedChamber

Python/Recursion/DecodedStringAtIndex.py

@@ -0,0 +1,50 @@
+# Definition for a binary tree node.
+import heapq
+import unittest
+
+# Read about enumerate in python
+from collections import defaultdict
+from typing import List
+
+class DecodedStringAtIndex(unittest.TestCase):
+
+    def decodeAtIndex(self, S: str, K: int) -> str:
+
+        count = 0
+        i = 0
+        curr = ""
+        while i < len(S):
+            if count == K:
+                return S[i-1]
+            elif S[i].isalpha():
+                curr += S[i]
+                i += 1
+                count += 1
+            elif S[i].isdigit():
+                j = i
+                while j < len(S) and S[j].isdigit():
+                    j += 1
+                number = int(S[i:j])
+                multiplyLength = i * number
+                if multiplyLength > K:
+                    return self.decodeAtIndex(S[:i], K % i)
+                elif multiplyLength == K:
+                    return curr[-1]
+                else:
+                    curr = curr * number
+                    i = j
+                    count = multiplyLength
+
+        return ""
+
+    def test_Leetcode(self):
+        self.assertEqual("o", self.decodeAtIndex("leet2code3", 10))
+        self.assertEqual("h", self.decodeAtIndex("ha22", 5))
+        self.assertEqual("a", self.decodeAtIndex("a2345678999999999999999", 1))
+
+    def test_Edgecase(self):
+        self.assertEqual("t", self.decodeAtIndex("leet2code3", 8))
+        return
+
+if __name__ == '__main__':
+    unittest.main()