KPM 字符串查找 Java版

Knuth-Morris-Pratt 字符串查找算法，簡稱爲 “KMP算法”

import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.validation.constraints.NotNull;

public class KpmTest {
    private static final Logger log = LoggerFactory.getLogger(KpmTest.class);

    @Test
    public void test() {
        String ps = "aab";
        String target = "1gg2abababcabaabbca0";
        kmp(target, ps);
    }

    /**
     * <blockquote>
     * <pre>
     * 1. 首先獲取{@code ps}  的next[]
     * <p>
     * 例如 ：[0,1,0]
     * <p>
     * {@code target} caaab
     * {@code ps} aab
     * 1:caaab
     *    aab
     * 沒有相等的移動一位
     * 2:caaab
     *    aab
     * 有兩位相等 -> next[2]=0 爲0時 +1
     * 3:caaab
     *     aab
     * 匹配成功
     *
     * </pre></blockquote>
     *
     * @param target 目標字符串
     * @param ps     匹配字符串
     */
    public void kmp(String target, String ps) {

        int[] next = getNext(ps);
        char[] psChars = ps.toCharArray();
        char[] targetChars = target.toCharArray();
        log.info("next: {}", next);

        int index = -1;
        int i = 0;
        for (int j = 0; j < psChars.length; ) {
            if (i + j > targetChars.length - 1) {
                break;
            }
            if (targetChars[i + j] == psChars[j]) {
                ++j;
                if (j == psChars.length) {
                    index = i;
                }
            } else {
                i += next[j] == 0 ? 1 : next[j];
                j = 0;
            }
        }
        log.info("index: {}", index + 1);

    }

    /**
     * <blockquote><pre>
     * 例如：ababbc 獲取next[]
     * next[0] 默認爲0
     * 1：ababbc
     *     ababbc
     *    00
     * 總共匹配0 獲取移動量 next[0] 爲0是 自動加一
     * 2：ababbc
     *      ababbc
     *    0012
     * 總共匹配2 獲取移動量 next[2]=1
     * 3:ababbc
     *       ababbc
     *   00120
     * 總共匹配0 獲取移動量 next[0] 爲0是 自動加一
     * 4:ababbc
     *        ababbc
     *  001200
     *  結束
     * </pre></blockquote>
     *
     * @param ps
     * @return
     */
    public int[] getNext(@NotNull String ps) {
        int length = ps.length();
        char[] chars = ps.toCharArray();
        int[] next = new int[length];
        next[0] = 0;
        if (length > 1) {
            int i = 1;
            for (int j = 0; i + j < length; ) {
                if (chars[i + j] == chars[j]) {
                    next[i + j] = j + 1;
                    j++;
                } else {
                    i += next[j] == 0 ? 1 : next[j];
                    j = 0;
                }
            }
        }
        return next;
    }
}