KMP算法实现目标串与模式串匹配

//KMP算法实现字符串匹配 
//该算法保证字符比较次数不超过目标串字符长度的2倍 
#include <cstdlib>
#include <iostream>

using namespace std;
 
 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 
      int j=0;
      int q=next[0]=-1;
      --len;
      while(j<len)
      if(q==-1||p[q]==p[j])
      next[++j]=++q;
      else 
      q=next[q];
      } 

char const* kmp_find(char const*t,int tlen,char const*p,int plen,int const*next){
      int i=-1;
      int j=-1;
      while((i<tlen)&&(j<plen)){
        if((j==-1)||(t[i]==p[j])) {++i;++j;}
        else j=next[j];                        
                                }
      if(j==plen) return t+i-plen;
      else return 0;                               
                                      }
 
int main()
{   char a[100]="ahgdhjggabcabcabbacll";//用户自编目标串 
    char b[12]="abcabcabbac";//用户自编模式串 
    char const* t_;
    int next[11];//与b串的元素个数相同，不含null 
    compute_next(next,b,11);// 与b串的元素个数相同，不含null
    
    cout<<"target string:"<<endl;
    for(int i=0;a[i];i++)
     cout<<a[i];
      cout<<endl; cout<<endl; 
    cout<<"mode string:"<<endl;
    for(int i=0;b[i];i++)
     cout<<b[i];
      cout<<endl;cout<<endl; 
     
    cout<<"最大重叠度计算为："<<endl;
     for(int i=0;i<11;i++)
          cout<<"pi("<<i<<"):"<<next[i]<<endl;
      cout<<endl; 
          
    t_=kmp_find(a,100,b,11,next);
   if(!t_)
      cout<<"can not find mode string in target string!"<<endl;
      else 
      cout<<"the position of mode string in target string is:"<<t_-a+1<<endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}