kmp算法实现

kmp核心就是求next数组，而求next数组核心就是记住，next[i]保存的是模式串当前索引不匹配是下一个应该比较的索引

public class KMP {
    //p模式串
    public static int match(String p,String s){
        if(s.length()<p.length())
            return -1;
        int[] next = new int[p.length()];
        next[0] = -1;
        int j=-1;
        int i=0;
        while(i<p.length()-1){
            if(j==-1||p.charAt(i)==p.charAt(j)){
                j++;
                i++;
                next[i] = j;
                //next优化
                while(next[i]!=-1&&p.charAt(next[i])==p.charAt(i)){
                    next[i] = next[next[i]];
                }
            }else {
                j = next[j];
            }
        }
        i=0;
        j=0;
        while((s.length()-i>=p.length()-j)){
            if(j==-1||s.charAt(i)==p.charAt(j)){
                i++;
                j++;
                if(j==p.length()-1){
                    return i-p.length()+1;
                }
            }else {
                j=next[j];
            }
        }
        return -1;
    }
}