Create 91 Decode ways.cpp

Author: Meghak1

91 Decode ways.cpp

@@ -0,0 +1,29 @@
+class Solution {
+public:
+    int numDecodings(string s) {
+        int n=s.length();
+     if(n==0 || s[0]=='0') {
+        return 0;
+    }
+
+    int prev1=1,prev2=1;
+
+    for(int i=1;i<n;++i) 
+      {
+        int current=0;
+        if(s[i]!='0') {
+            current+=prev2;
+      }
+      int digits=stoi(s.substr(i-1,2));
+        if(digits>=10 && digits<=26) 
+        {
+            current+=prev1;
+        }
+
+        prev1=prev2;
+        prev2=current;
+    }
+
+    return prev2;
+    }
+};