feat: add decode ways solution

Author: mangodm-web

decode-ways/mangodm-web.py

@@ -0,0 +1,16 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        if s[0] == "0":
+            return 0
+
+        n = len(s)
+        dp = [0] * (n + 1)
+        dp[0], dp[1] = 1, 1
+
+        for i in range(2, n + 1):
+            if s[i - 1] != "0":
+                dp[i] += dp[i - 1]
+            if "10" <= s[i - 2 : i] <= "26":
+                dp[i] += dp[i - 2]
+
+        return dp[n]