Merge pull request neetcode-gh#844 from notauserx/Create-91-Decode-Wa…

…ys.cs

Create 91-Decode-Ways.cs

csharp/91-Decode-Ways.cs

@@ -0,0 +1,20 @@
+public class Solution {
+ public int NumDecodings(string s) {
+ List<int> dp = Enumerable.Repeat(1, s.Length + 1).ToList();
+
+ for(var i = s.Length - 1; i >= 0; i--) {
+ if (s[i] == '0') 
+ dp[i] = 0;
+ else 
+ dp[i] = dp[i + 1];
+
+ if (i + 1 < s.Length && (
+ s[i] == '1' || 
+ (s[i] == '2' && "0123456".Contains(s[i + 1]))
+ ))
+ dp[i] += dp[i + 2];
+ }
+
+ return dp[0];
+ }
+}