KMP字符串模式匹配学习

1.简单匹配算法：

 1     private int search(String source, String pattern) {
 2         int i = 0;
 3         int j = 0;
 4 
 5         int length = pattern.length();
 6         int lastIndex = source.length() - length;
 7 
 8         while (i <= lastIndex && j < length) {
 9             if (source.substring(i, i + length).equals(pattern)) {
10                 return i;
11             } else {
12                 i++;
13             }
14         }
15 
16         return -1;
17     }

 

 

2.KMP 算法学习

很重要的next[]获得方法：

 1     private void getNextVal(String pattern, int[] next) {
 2         // 求模式串T的next函数值并存入数组 next。
 3 
 4         int j = 0, k = -1;
 5         next[0] = -1;
 6         while (j < pattern.length()) {
 7             if (k == -1 || pattern.charAt(j) == pattern.charAt(k)) {
 8                 ++j;
 9                 ++k;
10 
11                 if (j < pattern.length() && k < pattern.length()) {
12                     if (pattern.charAt(j) != pattern.charAt(k)) {
13                         next[j] = k;
14                     } else {
15                         next[j] = next[k];
16                     }
17                 }
18 
19             } else {
20                 k = next[k];
21             }
22         }
23     }

进行匹配：

 

 1     private int searchKMP(String source, String pattern) {
 2         int i = 0;
 3         int j = 0;
 4 
 5         int[] next = new int[pattern.length() + 1];
 6         getNextVal(pattern, next);
 7 
 8         while (i < source.length() && j < pattern.length()) {
 9             if (source.charAt(i) == pattern.charAt(j)) {
10                 i++;
11                 j++;
12             } else {
13                 if (next[j] != -1) {
14                     j = next[j];
15                 } else {
16                     j = 0;
17                     i++;
18                 }
19             }
20         }
21 
22         if (j == pattern.length()) {
23             return i - j;
24         } else {
25             return -1;
26         }
27     }

 

 

 

参考：http://www.cppblog.com/oosky/archive/2006/07/06/9486.html

posted @ 2013-12-17 17:46  自由飞翔2012  阅读(284)  评论(0)  编辑  收藏  举报