字符串的查找--KMP算法

#include<iostream>

#include<string>

using namespace std;

int* get_next(string& s)

{

int i = 0, j = -1;

int* next = new int[s.size()];

next[0] = -1;

while (i < s.length() - 1)

{

if (j == -1 || s[i]==s[j])

{

i++;

j++;

next[i] = j;

}

else

{

j = next[j];

}

}

return next;

}

int kmp_index(string &Tag, string& Ptn, int pos)

{

int* next = get_next(Ptn);

int i = pos;

int j = 0;

int Tlen = Tag.size();

int Plen = Ptn.size();

while (i < Tlen && j < Plen)

{

if (j == -1 || Tag[i] == Ptn[j])

{

i++;

j++;

}

else

{

j = next[j];

}

}

if (j >= Plen)

return i - Plen;

else

return -1;

}

//测试程序：

int main()

{

char ch;

do{

string Tag, Ptn;

int pos;

cout << "输入主串：";

cin >> Tag;

cout << "输入子串：";

cin >> Ptn;

cout << "输入主串中开始进行匹配的位置（首字符位置为0）：";

cin >> pos;

int result = kmp_index(Tag, Ptn, pos);

if (result != -1)

cout << "主串与子串在主串的第" << result << "个字符（首字符的位置为0）处首次匹配" << endl;

else

cout << "无匹配子串" << endl;

cout << "是否继续测试（输入y或Y继续，任意其他键结束）：";

cin >> ch;

} while (ch == 'y' || ch == 'Y');

return 0;

}