decode ways

Author: SamTheKorean

decode-ways/samthekorean.py

@@ -0,0 +1,23 @@
+# TC : O(n)
+# SC : O(n)
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        if not s or s[0] == "0":
+            return 0
+
+        n = len(s)
+        dp = [0] * (n + 1)
+        dp[0] = 1
+        dp[1] = 1
+
+        for i in range(2, n + 1):
+            one_digit = int(s[i - 1])
+            two_digits = int(s[i - 2 : i])
+
+            if one_digit != 0:
+                dp[i] += dp[i - 1]
+
+            if 10 <= two_digits <= 26:
+                dp[i] += dp[i - 2]
+
+        return dp[n]