Optimized Algorithm for Pattern Searching

#include <bits/stdc++.h>
using namespace std;
  
/* A modified Naive Pattern Searching
algorithm that is optimized for the
cases when all characters of pattern are different */
void search(string pat, string txt)
{
    int M = pat.size();
    int N = txt.size();
    int i = 0;
  
    while (i <= N - M) {
        int j;
  
        /* For current index i, check for pattern match */
        for (j = 0; j < M; j++)
            if (txt[i + j] != pat[j])
                break;
  
        if (j == M) // if pat[0...M-1] = txt[i, i+1, ...i+M-1]
        {
            cout << "Pattern found at index " << i << endl;
            i = i + M;
        }
        else if (j == 0)
            i = i + 1;
        else
            i = i + j; // slide the pattern by j
    }
}
  
/* Driver code*/
int main()
{
    string txt = "ABCEABCDABCEABCD";
    string pat = "ABCD";
    search(pat, txt);
    return 0;
}