str_match.c

/****************************************/
/*Implementation of Levenshtein distance*/
/****************************************/

#include <stdlib.h>
#include <malloc.h>
#include <string.h>
#include "str_match.h"

int ldistance(char *s,char*t)
/*Compute levenshtein distance between s and t*/
{
  //Step 1
  int k,i,j,n,m,cost,*d,distance;
  n=strlen(s); 
  m=strlen(t);
  if(n!=0&&m!=0)
  {
    d=malloc((sizeof(int))*(m+1)*(n+1));
    m++;
    n++;
    //Step 2	
    for(k=0;k<n;k++)
	d[k]=k;
    for(k=0;k<m;k++)
      d[k*n]=k;
    //Step 3 and 4	
    for(i=1;i<n;i++)
      for(j=1;j<m;j++)
	{
        //Step 5
        if(s[i-1]==t[j-1])
          cost=0;
        else
          cost=1;
        //Step 6			 
        d[j*n+i]=minimum(d[(j-1)*n+i]+1,d[j*n+i-1]+1,d[(j-1)*n+i-1]+cost);
      }
    distance=d[n*m-1];
    free(d);
    return distance;
  }
  else 
    return -1; //a negative return value means that one or both strings are empty.
}

int minimum(int a,int b,int c)
/*Gets the minimum of three values*/
{
  int min=a;
  if(b<min)
    min=b;
  if(c<min)
    min=c;
  return min;
}