KMP查找算法

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45

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;
    }
}