KMP算法

1实现代码

public class KMP {

    public static  int[] KmpNext(String dest){
        //先准备一个Next数组，00000000，默认这个字符串不对称
        int[] next = new int[dest.length()];
        //开始推进Next
        for (int i = 1,j=0; i < dest.length(); i++) {
            while (j>0 && dest.charAt(i) != dest.charAt(j)){
                j = next[j - 1];
            }
            if (dest.charAt(i) == dest.charAt(j)){
                j++;
            }
            next[i] = j;
        }
        return next;
    }

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

        }
        return -1;
    }
    
    public static void main(String[] args) {
        String str1 = "abcabcabcd";
        String str2 = "abcabcd";

        int []array = KmpNext(str2);

        System.out.println( Kmp(str1,str2,array));

    }
}

2、实现结果

结果就是 3