KMP.cpp

void LPS(string pat, int M, int *lps);
 
int KMP(string pat, string txt)
{
    int M = pat.length();
    int N = txt.length(); 
    int lps[M];
    LPS(pat, M, lps);
    int i = 0, j = 0, count = 0;
    while (i < N) {
        if (pat[j] == txt[i]) {
            j++; i++;
        }
        if (j == M) {
            count++;
            j = lps[j-1];
        }
        else if (i < N && pat[j] != txt[i]) {
            if (j != 0)
                j = lps[j-1];
            else
                i = i+1;
        }
    }
    return count;
}
void LPS(string pat, int M, int *lps)
{
    int len = 0, i = 1; 
    lps[0] = 0;
    while (i < M) {
        if (pat[i] == pat[len]) {
            len++; lps[i] = len; i++;
        } else {
            if (len != 0) {
                len = lps[len-1];
            } else {
                lps[i] = 0;
                i++;
            }
        }
    }
}