1 //KMP算法实现字符串匹配
2 //该算法保证字符比较次数不超过目标串字符长度的2倍
3 #include <cstdlib>
4 #include <iostream>
5
6 using namespace std;
7
8 void compute_next(int* next,char const*p,int len){//计算模式串中元素序号j的左侧最大重叠度
9 int j=0;
10 int q=next[0]=-1;
11 --len;
12 while(j<len)
13 if(q==-1||p[q]==p[j])
14 next[++j]=++q;
15 else
16 q=next[q];
17 }
18
19 char const* kmp_find(char const*t,int tlen,char const*p,int plen,int const*next){
20 int i=-1;
21 int j=-1;
22 while((i<tlen)&&(j<plen)){
23 if((j==-1)||(t[i]==p[j])) {++i;++j;}
24 else j=next[j];
25 }
26 if(j==plen) return t+i-plen;
27 else return 0;
28 }
29
30 int main()
31 { char a[100]="ahgdhjggabcabcabbacll";//用户自编目标串
32 char b[12]="abcabcabbac";//用户自编模式串
33 char const* t_;
34 int next[11];//与b串的元素个数相同，不含null
35 compute_next(next,b,11);// 与b串的元素个数相同，不含null
36
37 cout<<"target string:"<<endl;
38 for(int i=0;a[i];i++)
39 cout<<a[i];
40 cout<<endl; cout<<endl;
41 cout<<"mode string:"<<endl;
42 for(int i=0;b[i];i++)
43 cout<<b[i];
44 cout<<endl;cout<<endl;
45
46 cout<<"最大重叠度计算为："<<endl;
47 for(int i=0;i<11;i++)
48 cout<<"pi("<<i<<"):"<<next[i]<<endl;
49 cout<<endl;
50
51 t_=kmp_find(a,100,b,11,next);
52 if(!t_)
53 cout<<"can not find mode string in target string!"<<endl;
54 else
55 cout<<"the position of mode string in target string is:"<<t_-a+1<<endl;
56 system("PAUSE");
57 return EXIT_SUCCESS;
58 }
