- Decode Ways #268

Author: ayosecu

decode-ways/ayosecu.py

@@ -0,0 +1,57 @@
+class Solution:
+    """
+        - Time Complexity: O(n), n = len(s)
+        - Space Complexity: O(n)
+    """
+    def numDecodingsDP(self, s: str) -> int:
+        if s[0] == "0":
+            return 0
+                
+        n = len(s)
+        dp = [0] * (n + 1)
+        # dp[0] => empty string => 1 case
+        # dp[1] => not 0 => 1 case (single digit)
+        dp[0], dp[1] = 1, 1
+
+        for i in range(2, n + 1):
+            one_digit = int(s[i - 1:i])
+            two_digit = int(s[i - 2:i])
+
+            if 1 <= one_digit <= 9:
+                dp[i] += dp[i - 1]
+            if 10 <= two_digit <= 26:
+                dp[i] += dp[i - 2]
+        
+        return dp[n]
+
+    """
+        - Time Complexity: O(n), n = len(s)
+        - Space Complexity: O(1)
+    """
+    def numDecodings(self, s: str) -> int:
+        if s[0] == "0":
+            return 0
+        
+        # Using two variables for checking single and double digit
+        prev2, prev1 = 1, 1
+
+        for i in range(1, len(s)):
+            current = 0
+            if s[i] != "0":
+                current += prev1
+            if 10 <= int(s[i - 1:i + 1]) <= 26:
+                current += prev2
+            prev2, prev1 = prev1, current
+        
+        return prev1    # prev1 = current
+    
+tc = [
+        ("12", 2),
+        ("226", 3),
+        ("06", 0)
+]
+
+for i, (s, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.numDecodings(s)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")