KMP算法实现查找字符串第一次出现的位置

package ten_algorithm.kmp;

import ten_algorithm.dynamic.KnapSack;

import java.util.Arrays;

/**
 * Author:jinpma
 * Date :2019/12/28
 */
public class KmpSearch
{
    public static void main(String[] args)
    {
        String str1 = "BBC ABCDAB ABCDABCDABDE";
        String str2 = "ABCDABD";
        KmpSearch k = new KmpSearch();
        int[] next = k.next(str2);
        int index = k.findIndex(str1, str2, next);
        System.out.println(index);

    }

    private int findIndex(String str1, String str2, int[] next)
    {
        int i, j;
        for (i = 0, j = 0; i < str1.length(); i++)
        {
            if (str1.charAt(i) == str2.charAt(j))
            {
                j++;
            } else
            {
                if (j > 0)//一开始若不==，j==0，j-1报错
                {
                    i = (i - j) + (j - next[j - 1]) - 1;//会有i++
                    j = 0;
                }
            }
            if (j == str2.length())
            {
                return i - j + 1;
            }
        }
        return -1;
    }


    public int[] next(String str2)
    {
        int next[] = new int[str2.length()];
        next[0] = 0;
        int i, j;
        for (i = 1, j = 0; i < str2.length(); i++)
        {
            if (str2.charAt(i) == str2.charAt(j))
            {
                j++;
            } else
            {
                j = 0;
            }
            next[i] = j;
        }
        return next;
    }
}

来源：CSDN

作者：tmax52HZ

链接：https://blog.csdn.net/tmax52HZ/article/details/103792733