KMP算法

public class KMP {
    //定义next取值
    public static int getnext(String t, String s, int[] next){
        next[0] = -1;//第一位初始为-1
        int i =0, j = -1;
        while(i<s.length()-1){
            if(j == -1){
                i++;
                j++;
                next[i] = j;
            }else{
                i++;
                for(int k = 1; k < i; k ++){
                    if(s.substring(0,k).equals(s.substring(i-k,i))){
                        int n = s.substring(0,k).length();//相同字段的长度为next值
                        next[i] = n;
                    }
                }
            }
        }
        return  kmp(t,s,next);
    }
    public static int kmp(String t, String s, int[] next){
        int i =0,j=0;
        while(i < t.length() && j < s.length()){
           if(j == -1 || t.charAt(i) == s.charAt(j)){
               i++;
               j++;
           }else{
               j = next[j];//子段从j位开始遍历
           }
        }
        if(j == s.length()){
            return i-s.length();
        }else{
            return -1;
        }
    }
    public static void main(String[] args) {
        String t = "abcababcaababcdasfsf";
      String s = "abcaababc";
      int[] next = new int[s.length()];
       int n = getnext(t,s,next);
       System.out.println(n);
    }
}