KMP

package L5;

public class L3 {

	static int[] next(String p) {
		int plen = p.length();
		char[] pc = p.toCharArray();
		int[] next = new int[plen];
		next[0] = -1;
		if (plen == 1)
			return next;
		next[1] = 0;
		int j = 1, k = next[j];
		while (j < plen - 1) {
			if (k < 0 || pc[j] == pc[k]) {
				next[++j] = ++k;
			} else {
				k = next[k];
			}
		}
		return next;
	}

	static int indexof(String s, String p) {
		int slen = s.length(), plen = p.length();
		int i = 0, j = 0;
		int[] next = next(p);
		while (i + plen < slen) {
			if (j == -1 || s.charAt(i) == p.charAt(j)) {
				i++;
				j++;
			} else {
				j = next[j];
			}
			if (j == plen)
				return i - j;
		}
		return -1;
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		String s = "abcdefabcde";
		String p = "def";
		int index = indexof(s, p);
		System.out.println(index);
	}

}