Boyer-Moore: Implement strStr() --- find a needle in a haystack

https://www.youtube.com/watch?v=izMKq3epJ-Q

Boyer-Moore algrt 关于skip的部分很重要

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

 

public class Solution {

    public int strStr(String haystack, String needle) {

        int[] hs = new int[256];

        int h=haystack.length();

        int n = needle.length();

        for(int i=0;i<256;i++){

            hs[i] = -1;

        }

        for(int i=0;i<n;i++){

            hs[needle.charAt(i)] = i;

        }

        int sk = 0;

        for(int i=0;i<h-n+1;i+=sk){

            sk = 0;

            for(int j=n-1;j>=0;j--){

                if(haystack.charAt(i+j)!=needle.charAt(j)){

                    sk = Math.max(1,j-hs[haystack.charAt(i+j)]);

                    break;

                }

            }

            if(sk==0) return i;

        }

        return -1;

    }

}