第一轮复习完毕，kmp走起

 1 #include<iostream>
 2 #include<string>
 3 #include<vector>
 4 using namespace std;
 5 
 6 int kmp_find(const string& target, const string& pattern)
 7 {
 8     const int target_length = target.size();
 9     const int pattern_length = pattern.size();
10     int * overlay_value = new int[pattern_length];
11     overlay_value[0] = -1;
12     int index = 0;
13     for (int i = 1; i<pattern_length; ++i)
14     {
15         index = overlay_value[i - 1];
16         while (index >= 0 && pattern[index + 1] != pattern[i])
17         {
18             index = overlay_value[index];
19         }
20         if (pattern[index + 1] == pattern[i])
21         {
22             overlay_value[i] = index + 1;
23         }
24         else
25         {
26             overlay_value[i] = -1;
27         }
28     }
29     //match algorithm start
30     int pattern_index = 0;
31     int target_index = 0;
32     while (pattern_index<pattern_length&&target_index<target_length)
33     {
34         if (target[target_index] == pattern[pattern_index])
35         {
36             ++target_index;
37             ++pattern_index;
38         }
39         else if (pattern_index == 0)
40         {
41             ++target_index;
42         }
43         else
44         {
45             pattern_index = overlay_value[pattern_index - 1] + 1;
46         }
47     }
48     if (pattern_index == pattern_length)
49     {
50         return target_index - pattern_index;
51     }
52     else
53     {
54         return -1;
55     }
56     delete[] overlay_value;
57 }
58 
59 int main()
60 {
61     string source = "ann6bcdanacadsannannabnna";
62     string pattern = "n6bcdan";
63     cout << kmp_find(source, pattern) << endl;
64     return 0;
65 }