字符串查找——蛮力和kmp

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 int force_search(char * s, int sl, char * p, int pl)
 6 {
 7     int i(0);
 8     while ( i + pl <= sl)
 9     {
10         int j(i), k(0);
11         while (k < pl)
12             if (s[j] == p[k])
13                 (j ++, k ++);
14             else
15                 break;
16         if (k == pl)
17             return i;
18         ++ i;
19     }
20     return -1;
21 }
22 
23 void print_int_arrays(int * arrays, int al)
24 {
25     for (int i(0); i < al; ++ i)
26         cout << arrays[i] << " ";
27     cout << endl;
28 }
29 
30 void print_char_arrays(char * arrays, int cl)
31 {
32     for (int i(0); i < cl; ++ i)
33         cout << arrays[i] << " ";
34     cout << endl;
35 }
36 
37 void get_nexts(char * p, int pl, int * nexts)
38 {
39     int j(0), k(-1);
40     nexts[0] = -1;
41     while (j < pl)
42         if (p[j] == p[k] || k == -1)
43             nexts[++ j] = ++ k;
44         else
45             k = nexts[k];
46 }
47 
48 int kmp_search(char * s, int sl, char * p, int pl)
49 {
50     int * nexts = new int[pl + 1];
51     get_nexts(p, pl, nexts);
52 
53     int i(0), j(0);
54     int indexbegin(0);
55     while (j < pl && i < sl)
56         if (s[i] == p[j])
57             (++ i, ++ j);
58         else
59         {
60             indexbegin = i - nexts[j]; 
61             0 == j ? ++ i :j = nexts[j];
62         }
63     delete[] nexts;
64     return j == pl ? indexbegin :  -1;
65 }
66 
67 
68 int main()
69 {
70     char * mstr = "aaabacaabacaabacabaabb";
71     char * pstr = "abacab";
72     
73     for (int i = 0; i < 18; ++ i)
74     {
75         pstr = mstr + i;
76         cout << "========================" << endl;
77         cout
78             << force_search(mstr, strlen(mstr), pstr, strlen(pstr))
79             << endl;
80         cout
81             << kmp_search(mstr, strlen(mstr), pstr, strlen(pstr))
82             << endl;
83     }
84 
85     return 0;
86 }