KMP 最优字符串查找算法

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import java.util.Arrays;

/**
 * User: yiminghe
 * Date: 2009-2-19
 * Time: 16:37:57
 */
public class Kmp {


    /**
     * index[i]  越小 ，滑动越多，匹配速度越快
     *
     * @param pattern
     * @return
     */
    private static int[] getFail(String pattern) {


        int[] index = new int[pattern.length()];
        index[0] = -1;
        int lengthP = pattern.length();

        for (int i = 1; i < lengthP; i++) {

            int cf = index[i - 1];
            while (pattern.charAt(cf + 1) != pattern.charAt(i) && cf >= 0) cf = index[cf];
            if (pattern.charAt(cf + 1) == pattern.charAt(i)) index[i] = cf + 1;
            else index[i] = -1;
        }
        return index;
    }

    public static int kmpFind(String target, String pattern) {
        int posP = 0;
        int posT = 0;
        int lenP = pattern.length();
        int lenT = target.length();
        int[] index = getFail(pattern);
        while (true) {
            while (posT < lenT && posP < lenP && target.charAt(posT) == pattern.charAt(posP)) {
                ++posT;
                ++posP;
            }
            if (posP == lenP) {
                return posT - lenP;
            }
            if (posT == lenT) return -1;
            if (posP == 0) ++posT;
            else
                posP = index[posP - 1] + 1;


        }
    }


    public static void main(String[] args) {
        //字符串从左开始1
        System.out.println(kmpFind("acabaabaabcacaabc", "abaabcac"));
    }
}