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. Here is the Code: Program in C++: #include<iostream> using namespace std; int totalNumberOfWays(char *a,int n) { if(isalpha(n)) return 1; if(a[0]=='0') return 0; int p=1,q=1,res=1; for(int i=1;i<n;i++) { int t = (a[i-1]-'0')*10+a[i]-'0'; if(t>=10&&t<=26) { if(t==10||t==20) res=p; else res=p+q; } else { if(t%10==0) return 0; else res=q; } p=q; q=res; } return res; } int main() { int t; cin>>t; while(t--) { int n; cin>>n; char a[n]; cin>>a; int now = totalNumberOfWays(a,n); cout<<now<<endl; } return 0; } Here is the Video: