Created 0092_Decode_Ways.py

LeetCode/0092_Decode_Ways.py

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+'''
+Problem:-
+A message containing letters from A-Z is being encoded to numbers using the following mapping:
+
+'A' -> 1
+'B' -> 2
+...
+'Z' -> 26
+Given a non-empty string containing only digits, determine the total number of ways to decode it.
+
+The answer is guaranteed to fit in a 32-bit integer.
+
+Example 1:
+
+Input: s = "12"
+Output: 2
+Explanation: It could be decoded as "AB" (1 2) or "L" (12).
+
+Example 2:
+
+Input: s = "226"
+Output: 3
+Explanation: It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).
+'''
+
+class Solution:
+ def numDecodings(self, s: str) -> int:
+ @lru_cache(None)
+ def dp(i):
+ if i == len(s):
+ return 1
+ ans = 0
+ if s[i] != '0':
+ ans += dp(i+1)
+ if s[i] == '1' and i+1< len(s):
+ ans += dp(i+2)
+ if s[i] == '2' and i+1 < len(s) and s[i+1] <= '6':
+ ans += dp(i+2)
+ return ans 
+ return dp(0)