Envío 2074

Código

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main() {
  string input;
  cin >> input;
  vector<int> prefix (input.length(), 0);
  int border = 0;
  for (int i = 1; i < input.length(); i++) {
	 while(border>0 and input[i] != input[border]) {
		border = prefix[border-1];
	 }
	 if (input[i] == input[border]) {
		border++;
	 } else {
		border = 0;
	 }
	 prefix[i] = border;
  }
  cout << prefix[input.length()-1] << endl;
  return 0;
}