Java Implementation of KMP Algorithm

KMP research 
reference: http://blog.csdn.net/v_july_v/article/details/7041827 
I have been doing KMP questions for several days, and I finally wrote it today. I can summarize what I have learned so many days, combined with After many versions, I think July is the best one. KMP is a classic algorithm that solves whether the pattern string has appeared in the text string, and if it appears, the earliest position. 
First of all, if this problem is solved by brute force method, there will be a lot of backtracking, and only move one bit at a time. If it does not match, move to the next bit and then judge, which wastes a lot of time. Therefore, the kmp method algorithm uses The information has been judged before, and a next array is used to save the length of the longest common subsequence before and after the pattern string. When backtracking, the position that has been matched before is found through the next array, which saves a lot of calculation time. 
Not much to say, the code: `

public class KMP {
    public static int kmp(String str, String dest,int[] next){//str文本串  dest 模式串
        for(int i = 0, j = 0; i < str.length(); i++){
            while(j > 0 && str.charAt(i) != dest.charAt(j)){
                j = next[j - 1];
            }
            if(str.charAt(i) == dest.charAt(j)){
                j++;
            }
            if(j == dest.length()){
                return i-j+1;
            }
        }
        return 0;
    }
    public static int[] kmpnext(String dest){
        int[] next = new int[dest.length()];
        next[0] = 0;
        for(int i = 1,j = 0; i < dest.length(); i++){
            while(j > 0 && dest.charAt(j) != dest.charAt(i)){
                j = next[j - 1];
            }
            if(dest.charAt(i) == dest.charAt(j)){
                j++;
            }
            next[i] = j;
        }
        return next;
    }
    public static void main(String[] args){
        String a = "ababa";
        String b = "ssdfgasdbababa";
        int[] next = kmpnext(a);
        int res = kmp(b, a,next);
        System.out.println(res);
        for(int i = 0; i < next.length; i++){
            System.out.println(next[i]);            
        }
        System.out.println(next.length);
    }
}

运行结果：9 
0 0 1 2 3 5 
其实kmp算法的核心代码就几行而已 
在匹配阶段，若是模式串和文本串相同，那就继续匹配下一位，若是不相同，就去找next数组记录的位置，继续匹配，这个也是kmp算法和普通暴力算法的主要区别，暴力是从头开始匹配，而kmp通过next数组，发现前面可以跳过大量重复计算的东西。 
下面讲一下，next数组的计算方法： 
next数组的计算主要跟模式串有关，与文本串并没有关系，因为，模式串前后公共最长子序列。这样才会让我们跳过大量的重复计算 
next数组的主要实现方法有很多，就是要找到前后最长公共子序列的长度 比如： 
ababa： 
模式串的各个子串： 前缀： 后缀： 最大公共元素长度 
a 0 
ab a b 0 
aba a ab a ba 1 
abab a ab aba b ab bab 2 
ababa a ab aba abab a ba aba baba 3 
如上图，next数组中的元素就是 0 0 1 2 3 ； 
所以，kmp算法的核心就是计算next数组。理解到这里，就明白kmp算法了，就不会看一次忘一次了！ 
kmp算法的核心时间复杂度就是O（m+n）