[006] largest_common_substring

[Description] Given two different strings, find the largest successive common substring.

e.g.　　str1[]="qwertyuiopasdfgh";　　str2[]="jhdfgqwertyudfxcv";

　　      LCsubstr[]="qwertyu";

[Thought] show the correspondence result of this two strings from the 2-D array of 'record[][]', and find the longest non-zero diagonal elements. To save the auxiliary space, we can use only 1-D array 'record[]' to implement. 　　O(n^2)　　O(m)

[Implementation] C code:

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

 char* LCS(char longer[], char shorter[])
 {
         int longer_len=strlen(longer);
         int shorter_len=strlen(shorter);
         int record[shorter_len];
         int i,j,max_len=,substr_end=,substr_begin;

         for(i=;i<longer_len;i++)
         {
                 for(j=shorter_len-;j>=;j--)
                 {
                         if(longer[i]==shorter[j])
                         {
                                 if(==i || ==j)
                                 {
                                         record[j]=;
                                 }
                                 else
                                 {
                                         record[j]=record[j-]+;
                                 }
                         }
                         else
                         {
                                 record[j]=;
                         }

                         if(record[j]>max_len)
                         {
                                 max_len=record[j];
                                 substr_end=j;
                         }
                 }
         }

         substr_begin=substr_end-max_len+;

 //      char substr[max_len];
         char* substr=(char*)malloc(max_len);
         for(i=;i<max_len;i++)
         {
                 substr[i]=shorter[substr_begin+i];
         }
         return substr;
 }

 int main()
 {
         char longer[]="asdfghjklqwertyyuio";
         char shorter[]="zxvsdffghwerxv";

         printf("The longer str:\n\t%s\n",longer);
         printf("The shorter str:\n\t%s\n",shorter);
         printf("The lagest common str:\n\t%s\n",LCS(longer,shorter));
         return ;
 }