solved decode-ways.

Author: sangbeenmoon

combination-sum/sangbeenmoon.py

@@ -18,9 +18,3 @@ def go(self, i:int, candidates: List[int], nums: List[int], sum_: int, target: i
                 nums.append(candidates[j])
                 self.go(j, candidates, nums, sum_ + candidates[j], target)
                 nums.pop()
-
-        
-
-
-            
-

decode-ways/sangbeenmoon.py

@@ -0,0 +1,36 @@
+# idea
+# 마지막 두자리 수가 독립 가능 -> dp[i] = dp[i-1] + dp[i-2]
+#   마지막 한자리 수가 독립 가능 -> dp[i] = dp[i-1]
+#     위 두 케이스 모두 불가능 -> 0 반환
+# TC : O(n)
+# SC : O(n)
+
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        dp = [1] * len(s)
+
+        if s[0] == '0':
+            return 0
+        
+        if '1' <= s[0] and s[0] <= '9':
+            dp[0] = 1
+
+        for i in range(1, len(s)):
+            target = s[i-1:i+1]
+            
+            if int(s[i]) != 0 and 10 <= int(target) and int(target) <= 26:
+                dp[i] = dp[i-1] + dp[i-2]
+                continue
+
+            if int(s[i]) == 0 and 10 <= int(target) and int(target) <= 26:
+               dp[i] = dp[i-2]
+               continue
+
+            target = s[i]
+            if 1 <= int(target) and int(target) <= 9:
+                dp[i] = dp[i-1]
+                continue
+
+            return 0
+        
+        return dp[len(s) - 1]