1.涉及知識部分匹配表
A 0
AB 字首A 字尾B 公共部分長度0
ABA
字首：A AB 字尾：BA A 公共部分A，長度為1
[0,0,1]



package com.hy.tenalgorithm;

import java.util.Arrays;

/**
 * @author hanyong
 * @date 2020/7/16 1:04
 */
public class KMPAlgorithm {
    public static void main(String[] args) {

        String str1 = "BBC ABCDAB ABCDABCDABDE";
        String str2 = "ABCDABD";
 
        //String str2 = "BBC";

        int[] next = kmpNext("ABCDABD"); //[0, 1, 2, 0]
        System.out.println("next=" + Arrays.toString(next));

        int index = kmpSearch(str1, str2, next);
        System.out.println("index=" + index); // 15了

    }

    /**
     * @param str1 源字串
     * @param str2 子串
     * @param next 子串的部分匹配表
 
     * @return
     */
    public static int kmpSearch(String str1, String str2, int[] next) {

        for (int i = 0, j = 0; i < str1.length(); i++) {
            while (j > 0 && str1.charAt(i) != str2.charAt(j)) {
                j = next[j - 1];
            }
            if (str1.charAt(i) == str2.charAt(j)) {
 
                j++;
            }
            if (j == str2.length()) {
                return i - j + 1;
            }
        }
        return -1;
    }

    /**
     * 獲取一個字串的部分匹配值表
     *
     * @param str
     * @return
     */
    public static int[] kmpNext(String str) {
        int[] next = new int[str.length()];
        next[0] = 0;

        for (int i = 1, j = 0; i < str.length(); i++) {
            while (j > 0 && str.charAt(i) != str.charAt(j)) {
                j = next[j - 1];
            }
            if (str.charAt(i) == str.charAt(j)) {
                j++;
            }
            next[i] = j;
        }

        return next;
    }
}