javakmp算法实现

KMP算法是一种改进的字符串匹配算法，它的核心是利用匹配失败后的信息，尽量减少模式串与主串的匹配次数以达到快速匹配的目的。在Java中，可以通过以下代码实现KMP算法：

public class KMP {
    public static int KMP(String Str, String Sub, int pos){
        if (Str == null || Sub == null){
            return -1;
        }
        if (pos >= Str.length() || pos < 0){
            return -1;
        }
        int i = pos;
        int j = 0;
        int[] next = new int[Sub.length()];
        getNext(next, Sub);
        while(i < Str.length() && j < Sub.length()){
            if (j == -1 || Str.charAt(i) == Sub.charAt(j)){
                i++;
                j++;
            } else {
                j = next[j];
            }
        }
        if (j >= Sub.length()){
            return i - j;
        } else {
            return -1;
        }
    }
    
    public static void getNext(int[] next, String sub){
        next[0] = -1;
        next[1] = 0;
        int i = 2;
        int k = 0;
        while(i < next.length){
            if (k == -1 || sub.charAt(k) == sub.charAt(i-1)){
                next[i] = k + 1;
                i++;
                k++;
            } else {
                k = next[k];
            }
        }
    }
}