leetcode 28 KMP 简单实现strstr()

AC代码如下，有空优化：

class Solution {
    public int strStr(String s, String p) {
        if(s==null||p==null)
            return -1;
        if(s.length()==0&&p.length()==0)
            return 0;
        if(p.length()==0)
            return 0;
        int i=0;
        int j=0;
        int[] prefix=new int[p.length()];
        int[] next=new int[p.length()];
        getNext(p,prefix,next);
        while(i<s.length()&&j<p.length()){
            if(j==-1||s.charAt(i)==p.charAt(j)){
                i++;
                j++;
            }else
                j=next[j];
        }
        if(j==p.length())
            return i-j;
        else
            return -1;
    }
    public void getNext(String p,int[] prefix,int[] next){
        int len=p.length();
        for(int i=1;i<len;i++){
            int k=prefix[i-1];
            while(p.charAt(i)!=p.charAt(k)&&k!=0){
                k=prefix[k-1];
            }
            if(p.charAt(i)==p.charAt(k))
                prefix[i]=k+1;
            else
                prefix[i]=0;
        }
        next[0]=-1;
        for(int i=1;i<next.length;i++){
            next[i]=prefix[i-1];
        }
    }  
}

详细解释链接：https://blog.youkuaiyun.com/God_Mood/article/details/100109127