【编程练习】kmp算法代码

时间:2023-02-05 04:03:01

代码来自:

http://blog.csdn.net/v_JULY_v

#include "StdAfx.h"
#include <iostream> using namespace std; void GetNextval(char* p, int* next)
{
int pLen = strlen(p);
next[0] = -1;
int k = -1;
int j = 0;
while (j < pLen - 1)
{
//p[k]表示前缀,p[j]表示后缀
if (k == -1 || p[j] == p[k])
{
++j;
++k;
//较之前next数组求法,改动在下面4行
if (p[j] != p[k])
next[j] = k; //之前只有这一行
else
//因为不能出现p[j] = p[ next[j ]],所以当出现时需要继续递归,k = next[k] = next[next[k]]
next[j] = next[k];
}
else
{
k = next[k];
}
}
} int KmpSearch(char* s, char* p)
{
int i = 0;
int j = 0;
int sLen = strlen(s);
int pLen = strlen(p);
int* next = new int[pLen]; GetNextval(p,next);
while (i < sLen && j < pLen)
{
//①如果j = -1,或者当前字符匹配成功(即S[i] == P[j]),都令i++,j++
if (j == -1 || s[i] == p[j])
{
i++;
j++;
}
else
{
//②如果j != -1,且当前字符匹配失败(即S[i] != P[j]),则令 i 不变,j = next[j]
//next[j]即为j所对应的next值
j = next[j];
}
}
if (j == pLen)
return i - j;
else
return -1;
} int main()
{
char* s = "a is a good girl";
char* p = "good"; cout<<"we can find the word in the position:"<<KmpSearch(s,p)<<endl;
getchar();
return 0;
}