Solution Decode ways

Author: doitduri

decode-ways/doitduri.swift

@@ -0,0 +1,31 @@
+class Solution {
+    func numDecodings(_ s: String) -> Int {
+         if s.first == "0" {
+            return 0
+        }
+
+        if s.count == 1 {
+            return 1
+        }
+
+        var tables = Array(repeating: 0, count: s.count+1)
+        let chars = Array(s)
+        tables[0] = 1
+        tables[1] = 1
+        
+        for i in 2...s.count {
+            if chars[i-1] != "0" {
+                tables[i] += tables[i-1]
+            }
+
+            if let twoDigit = Int(String(chars[i-2...i-1])) {
+                if 10 <= twoDigit && twoDigit <= 26 {
+                    tables[i] += tables[i-2]
+                }
+            }
+            
+        }
+        
+        return tables[s.count]
+    }
+}