Total Decoding Messages

Task: Number of decoding messages from given number(in the form of string), The decoding way is 1 with A, 2 with B ... 26 with Z.

Example:

Input:

1

123

Output:

3 // ABC,LC and AW.

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Here is the Code:

Program in C++:

1. #include<iostream>
2. using namespace std;
3. int totalNumberOfWays(char *a,int n)
4. {
5.     if(isalpha(n)) return 1;
6.     if(a[0]=='0') return 0;
7.     int p=1,q=1,res=1;
8.     for(int i=1;i<n;i++)
9.     {
10.         int t = (a[i-1]-'0')*10+a[i]-'0';
11.         if(t>=10&&t<=26)
12.         {
13.             if(t==10||t==20) res=p;
14.             else res=p+q;
15.         }
16.         else
17.         {
18.             if(t%10==0) return 0;
19.             else res=q;
20.         }
21.         p=q;
22.         q=res;
23.     }
24.     return res;
25. }
26. int main()
27.  {
28. int t;
29. cin>>t;
30. while(t--)
31. {
32.     int n;
33.     cin>>n;
34.     char a[n];
35.     cin>>a;
36.     int now = totalNumberOfWays(a,n);
37.     cout<<now<<endl;
38. }
39. return 0;
40. }

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Here is the Video: