feat: 91. Decode Ways

decode-ways/HodaeSsi.py

@@ -0,0 +1,28 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        dp = []
+        if (s[0] == '0'):
+            return 0
+        dp.append(1)
+
+        for idx, _ in enumerate(s):
+            if idx == 0:
+                continue
+            if s[idx] == '0':
+                if s[idx-1] == '1' or s[idx-1] == '2':
+                    if idx == 1:
+                        dp.append(1)
+                    else:
+                        dp.append(dp[idx-2])
+                else:
+                    return 0
+            elif s[idx-1] == '1' or (s[idx-1] == '2' and (s[idx] >= '1' and s[idx] <= '6')):
+                if idx == 1:
+                    dp.append(2)
+                else:
+                    dp.append(dp[idx-1] + dp[idx-2])
+            else:
+                dp.append(dp[idx-1])
+
+        return dp[-1]
+