kmp算法Java版

Fri, 05 Nov 2021 23:31:27 +0800

KMP查找算法

import java.util.Arrays;

public class getstr {
    public static void main(String[] args) {
        String txt = "qwertyqwertyuisdgfsdnhjt";
        String gol = "sdgfsdn";
        int i = kmp(txt,gol);
        System.out.println("matchPoint: " + i);
    }
    static int kmp(String str1, String str2){
        int [] ary =getnext(str2);
        System.out.println(Arrays.toString(ary));

        for(int i =0,j = 0; i < str1.length();i++){
            while(j > 0 && str1.charAt(i) != str2.charAt(j) ){
                j = ary[j-1];
            }
            if(str1.charAt(i) == str2.charAt(j)){
                j++;
            }
            if(j == str2.length()){
//                System.out.println("i = "+i+"\nj = "+j);
                return i-j+1;
            }
        }
        return -1;
    }
    static int [] getnext(String str2){
        int [] ary = new int[str2.length()];
        ary[0] = 0;
        for(int i = 1, y = 0; i < str2.length(); i++ ){

            while(y > 0 && str2.charAt(i) != str2.charAt(y)){
                y-=1;
            }
            if(str2.charAt(i) == str2.charAt(y)){
                y++;
            }
            ary[i] = y;
        }

        return ary;
    }
}

其实一开始我也没有咋明白,但是后来我找到了下面这个文章 smoke_zl_图解kmp算法-通俗易懂kmp算法我就一下捂了,这个查找算法太妙了,就靠这一个数组,就可以实现快速查找不回溯

Kmp on JokemeBlog

kmp算法Java版

KMP查找算法