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package com.lyd;

/**
 * @author lyd
 * @date 2022/10/20 9:52
 * @desciption: 字符串匹配KMP
 */
public class code_KMP {


    public static void main(String[] args) {
        String s1 = "adcadadadasw";
        String dp = "cad";
        System.out.println(getKmp(s1, dp));

    }

    public static int getKmp(String s ,String dp) {
        if (s == null || dp == null || s.length() < 1 || dp.length() < 1) {
            return -1;
        }
        char[] str1 = s.toCharArray();
        char[] str2 = dp.toCharArray();
        int i1 = 0;
        int i2 = 0;
        int[] next = getNextArray(str2);
        while (i1 < str1.length && i2 < str2.length) {
            if (str1[i1] == str2[i2]) {
                i1++;
                i2++;
            } else if (next[i2] == -1) {
                i1++;
            }else
                i2 = next[i2];
        }
        return i2 == str2.length ? i1-i2 : -1;
    }

    public static int[] getNextArray(char[] cdp) {
        if (cdp.length == 1) {
            return new int[] {-1};
        }
        int[] next = new int[cdp.length];
        next[0] = -1;
        next[1] = 0;
        int i = 2;
        int cn = 0;
        while(i < next.length){
            if (cdp[i-1] == cdp[cn]) {
                next[i++] = ++cn;
            }else if(cn > 0) {
                cn =  next[cn];
            }else
                next[i++] = 0;
        }
        return next;
    }

}