关于KMP的讲解请参考上篇《三步学通KMP》(https://blog.csdn.net/helloworldchina/article/details/104465772),这里笔者仅补充一下C++代码的实现,见下:
1 next[]数组代码:
int* KmpNext(string str)
{
int* next = new int[str.size()];
next[0] = 0;
for(int j = 1,k = 0; j < str.size(); j++)
{
while(k > 0 && str[k] != str[j])
{
k = next[k - 1];
}
if(str[j] == str[k])
{
k++;
}
next[j] = k;
}
return next;
}
2 kmp代码
int KMP(string s, string t,int* next)
{//s主串 t 模式串
for(int i = 0, j = 0; i < s.size(); i++)
{
while(j > 0 && s[i] != t[j])
{
j = next[j - 1]; //下一个匹配位为next数组的第j-1位
}
if(s[i] == t[j])
{
j++;//主串通过i进行加1,模式串通过j加1
}
if(j == t.size())
{
return i-j+1;//返回匹配位置
}
}
return -1;
}
3 打印next[]数组代码
void PrintNext(string s)
{
std::cout << "********************" << std::endl;
int *nextI=NULL;
nextI = KmpNext(s);
std::cout << "模式串:'"+s+"'的next[]数组为:[";
for(int i = 0; i < (s.size()); i++)
{
std::cout<<*(nextI+i)<<" ";
}
std::cout<<"]"<<std::endl;
std::cout<<"模式串长度为:"+std::to_string(s.size())+" "<<std::endl;
}
4 主函数代码
int main()
{
//std::cout << "Hello, World!" << std::endl;
string s = "CDFGFABABAFABABAAAQWEDC";
string t = "ABABAA";
int* next = KmpNext(t);
int res = KMP(s, t,next);
if (res!=-1)
{
std::cout<<"起始位置为:"+std::to_string(res)+" "<<std::endl;;
}
else std::cout<<"主串中不包含字符串:"+t<<std::endl;
PrintNext("ABCDABD");
PrintNext("ABABAA");
PrintNext("ABAABCAC");
return 0;
}
5运行结果