基本算法——字符串查找之KMP算法

 1 #include <iostream>
 2 #include <string>
 3 #include <vector>
 4 #include <stdexcept>
 5 using namespace std;
 6 
 7 void get(const string &s, vector<int> &next)
 8 {
 9     int i = 0, j = -1;
10     next.push_back(-1);
11 
12     while(i < s.size() - 1)
13     {
14         if(j == -1 || s[i] == s[j])
15         {
16             ++ i;
17             ++ j;
18             if(s[i] != s[j])
19                 next.push_back(j);
20             else
21                 next.push_back(next[j]);
22         }
23         else
24             j = next[j];
25     }
26 }
27 
28 int kmp(const string &s, const string &d)
29 {
30     vector<int> next;
31     get(d, next);
32 
33     int i = 0, j = 0;
34     while(i < s.size() && j < d.size())
35     {
36         if(j == -1 || s[i] == d[j])
37         {
38             ++ i;
39             ++ j;
40         }
41         else
42             j = next[j];
43     }
44 
45     if(j >= d.size())
46         return i - d.size();
47     else
48         return -1;
49 }
50 
51 int main(int argc, const char *argv[])
52 {
53     string s("ababcabcacbab");
54     string d("abcac");
55 
56     int i = kmp(s, d);
57     if(i == -1)
58         cout << "false" << endl;
59     else
60         cout << i << endl;
61     return 0;
62 }