字符串匹配KMP算法实现

#include <stdio.h>
#include <string.h>
int KMP(char* s, char* pattern, int start, int next[]);
void get_new_next(char* pattern, int next[]);

int main()
{
int n;
char* s= "lakgjkaglamdaltjie";
char* pattern= "lamd";
int next[5];    //长度为strlen(pattern)+1
int start = 0;  //从start处开始搜索字符串s
get_new_next(pattern, next);
n = KMP(s, pattern, start, next);
printf("%d\n",n);
return 0;
}

//返回pattern在字符串s中匹配的第一个位置，例如：本例返回3
int KMP(char* s, char* pattern, int start, int next[])
{
int i = start, j = 1;
while (i<=(int)strlen(s) && j<=(int)strlen(pattern))
{
if(j==0 || s[i]==pattern[j-1])  //找到第一个匹配的字符，然后每次移动1位继续匹配
{
i++;
j++;
}
else
j = next[j];    //匹配失败，则查找部分匹配表，移动若干位
}
if(j>(int)strlen(pattern))
return i-strlen(pattern)+1;
else
return -1;  //Not found
}

//优化后的get_new_next函数(构造next[]的部分匹配表)
void get_new_next(char* pattern, int next[])
{

int k=-1,j=0;
next[0]=-1;
while (pattern[j]!='\0')  //循环直到pattern遇到结束符
{
//如果j的前面k个字符与开头的k个字符不相等
while(k!=-1 && pattern[k]!=pattern[j])
k = next[k];
j++;
k++;
//如果j的前面k个字符与开头的k个字符相等
if(pattern[k] == pattern[j])
next[j] = next[k];
else
next[j] = k;    //pattern[k]!=pattern[j](1<=k<j)
}

}