字符串匹配（模式匹配）KMP BM

最新推荐文章于 2016-05-08 13:40:00 发布

原创最新推荐文章于 2016-05-08 13:40:00 发布 · 536 阅读

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#string #算法 #search #build #table #up

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本文详细介绍了KMP算法和BM算法在字符串搜索中的应用，包括算法原理、实现步骤以及实例演示。KMP算法通过构建失配表来避免无效匹配的重复检查，而BM算法则利用模式和文本的前缀后缀特性进行高效搜索。

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text字符串中找到pat模式串。

//KMP算法

#include <string.h>

void setup(char pat[], int fail[])
{
int length = strlen(pat);
int i, j;

     fail[0] = -1;
     for (i = 1; i < length; i++) {
          for (j=fail[i-1]; j>=0 && pat[j+1]!=pat[i]; j=fail[j])
               ;
          fail[i] = (j < 0 && pat[j+1] != pat[i]) ? -1 : j+1;
     }
}

int KMP(char text[], char pat[], int fail[])
{
     int t_length = strlen(text);
     int p_length = strlen(pat);
     int t, p;

     setup(pat, fail);        /* build up the fail func. */
     for (t = p = 0; t < t_length && p < p_length; )
          if (text[t] != pat[p]) /* if not match ...      */
               if (p > 0)     /* is it the 1st location? */
                    p = fail[p-1] + 1; /* no, shift right */
               else
                    t++;      /* or match next in text[] */
          else
               t++, p++;      /* matched, advance both    */
     return (p >= p_length) ? t - p_length : -1;
}

/* ------------------------------------------------------ */

#include <stdio.h>

#define MAXSIZE 100

void main(void)
{
     char text[MAXSIZE];
     char pat[MAXSIZE];
     int   fail[MAXSIZE];
     int   answer, i;

     printf("\nKnuth-Morris-Pratt String Search Program");
     printf("\n========================================");
     printf("\n\nText String ------> ");
     gets(text);
     printf( "\nPattern String ---> ");
     gets(pat);

     if ((answer = KMP(text, pat, fail)) >= 0) {
          printf("\n ");
          for (i = 1; i <= 6; i++)
               printf("         %1d", i);
          printf("\n");
          for (i = 1; i <= 6; i++)
               printf("0....5....");
          printf("0");
          printf("\n%s\n", text);
          for (i = 0; i < answer; i++)
               printf(" ");
          printf("%s", pat);
          printf("\n\nPattern Found at location %d", answer);
     }
     else
          printf("\nPattern NOT found");
}

//BM算法

#include <string.h> /* for strlen() */

#define NOT_FOUND -1

void get_jump(unsigned char [], int []);
int BM(unsigned char [], unsigned char []);

int BM(unsigned char text[], unsigned char pat[])
{
     int jump_tab[256];
     int t_len = strlen(text);
     int p_len = strlen(pat);
     int i, j, k;

     get_jump(pat, jump_tab); /* compute the jump table   */
     for (i = p_len - 1; i < t_len; ) { /* comp. downward */
          for (j=p_len-1, k=i; j >= 0 && text[k] == pat[j]; k--,j--)
               ;
          if (j < 0)          /* if pat[] exhausted ?     */
               return k + 1; /* YES, pattern found.      */
          else                /* NO, update using jump_tab*/
               i += jump_tab[text[i]];
     }
     return NOT_FOUND;        /* text[] exhausted.        */
}

void get_jump(unsigned char pat[], int jump_tab[])
{
int length = strlen(pat);
int i;

     for (i = 1; i < 256; i++) /* assume length is the gap*/
          jump_tab[i] = length;
     for (i = 0; i < length - 1; i++) /* now adjust them. */
          jump_tab[(int)pat[i]] = length - i - 1;
}

/* ------------------------------------------------------ */

#include <stdio.h>
#include <stdlib.h>

#define MAXSIZE 100

void main(void)
{
     unsigned char text[MAXSIZE];
     unsigned char pat[MAXSIZE];
     int            answer, i;

     printf("\nBoyer-Moore String Searching Program");
     printf("\n====================================");
     printf("\n\nText String    --> ");
     gets(text);
     printf( "\nPattern String --> ");
     gets(pat);

     if ((answer = BM(text, pat)) >= 0) {
          printf("\n ");
          for (i = 1; i <= 6; i++)
               printf("         %1d", i);
          printf("\n");
          for (i = 1; i <= 6; i++)
               printf("0....5....");
          printf("0");
          printf("\n%s\n", text);
          for (i = 0; i < answer; i++)
               printf(" ");
          printf("%s", pat);
          printf("\n\nPattern Found at location %d", answer);
     }
     else
          printf("\nPattern NOT FOUND.");
}