数据结构字串的模式匹配 KMP算法

深碍√TFBOYSˉ_ 2022-09-19 01:44 136阅读 0赞

#include <stdio.h>
    #include <stdlib.h>
    
    #define OK          1
    #define ERROR       0
    #define OVERFLOW    -2
    
    typedef struct
    {
    	char *ch;
    	int length;
    }String;
    
    void Init_String(String &T)
    {
    	T.ch = NULL;
    	T.length = 0;
    }
    
    int StrAssign(String &T, char *chars)
    {
    	int i;
    	int len;
    	char *p = chars;
    	if (T.ch)
    	{
    		free(T.ch);
    	}
    	for (len = 0;*p != '\0'; ++len,++p);
    	if (!len)
    	{
    		T.ch = NULL;
    		T.length = 0;
    	}
    	else
    	{
    		T.ch = (char *)malloc(len * sizeof(char));
    		if (!T.ch)
    		{
    			exit(OVERFLOW);
    		}
    		for (i=0; i<len; i++)
    		{
    			T.ch[i] = chars[i];
    		}
    		T.length = len;
    	}
    	return OK;
    }
    
    
    
    void get_next(String T, int next[])
    {
    	int i = 0;
    	int j = -1;
    	next[0] = -1;
    	while (i<T.length)
    	{
    		if (j == -1 || T.ch[i] == T.ch[j])
    		{
    			++i;
    			++j;
    			next[i] = j;
    		}
    		else
    		{
    			j = next[j];
    		}
    	}
    }
    
    
    int Index_KMP(String S, String T, int pos)
    {
    	int i = pos;
    	int j = -1;
    	int next[255];
    	get_next(T,next);
    	while (i<S.length  && j <T.length )
    	{
    		if (j == -1 || S.ch[i] == T.ch[j])
    		{
    			++i;
    			++j;
    		}
    		else
    		{
    			j = next[j];
    		}
    	}
    	if (j == T.length )
    	{
    		return i-T.length + 1 ;
    	}
    	else
    		return 0;
    }
    
    
    
    
    int main()
    {
    	String S,T;
    	Init_String(S);
    	Init_String(T);
    	StrAssign(S,"abcdefghijklmm");
    	StrAssign(T,"cdef");
    	printf("%d\n",Index_KMP(S,T,0));
    	return 0;
    }