Why this problem is given in dp section?

#1

this is not a dp problem

#2

This is a dp problem only.

long long int countStrings(int n)
{
long long int a[n+1], b[n+1];

a[1] = b[1] = 1; 
for (int i = 2; i <= n; i++) 
{ 
    a[i] = a[i-1] + b[i-1]; 
    b[i] = a[i-1]; 
} 
return a[n] + b[n];

}
This is dp only

#3

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