Knuth–Morris–Pratt Algorithm

Knuth–Morris–Pratt (a.k.a KMP Algorithm) is a string search algorithm. it searches for occurrences of a sub-string within a main-string by employing the observation that when a mismatch occurs, the word itself embodies sufficient information to determine where the next match could begin, thus bypassing re-examination of previously matched characters.

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• PHP

									/*****Please include following header files*****/
// string
// vector
/***********************************************/

/*****Please use following namespaces*****/
// std
/*****************************************/

static void ComputeLPSArray(string pat, int m, int* lps) {
	int len = 0;
	int 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++;
			}
		}
	}
}

static vector<int> SearchString(string str, string pat) {
	vector<int> retVal;
	int M = pat.length();
	int N = str.length();
	int i = 0;
	int j = 0;
	int* lps = new int[M];

	ComputeLPSArray(pat, M, lps);

	while (i < N)
	{
		if (pat[j] == str[i])
		{
			j++;
			i++;
		}

		if (j == M)
		{
			retVal.push_back(i - j);
			j = lps[j - 1];
		}

		else if (i < N && pat[j] != str[i])
		{
			if (j != 0)
				j = lps[j - 1];
			else
				i = i + 1;
		}
	}

	delete[] lps;
	
	return retVal;
}
								

Example

									string data = "the quick brown fox jumps over the lazy dog";
vector<int> value = SearchString(data, "the");
								

Output

									0
31