Find the prefix values

// CPP program to find length of the
// longest prefix which is also suffix
#include <bits/stdc++.h>
using namespace std;
 
// Function to find largest prefix 
// which is also a suffix
int largest_prefix_suffix(const std::string 
                                      &str) 
{
   
  int n = str.length();
   
  // if n is less than 2
  if(n < 2) {
    return 0;
  }
 
  int len = 0;
  int i = (n + 1)/2;
   
  // Iterate i till n
  while(i < n)
  {
     
    // If str[i] is equal to 
    // str[len]
    if(str[i] == str[len]) 
    {
      ++len;
      ++i;
    }
    else
    {
      i = i - len + 1;
      len = 0;
    }
  }
   
  // Return len
  return len;
 
}
 
// Driver code
int main() 
{
     
  string s = "blablabla";
 
  // Function Call
  cout << largest_prefix_suffix(s);
  return 0;
}