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Thread: find LCS

  1. #1
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    Default find LCS

    Hey I have a algoritm
    that should get the longest comnon subseqquence
    between two strings
    public class Find {
     
    public static String find(String str1, String str2)
    {
    int i, j;
    int m = str1.length();
    int n = str2.length();
     
    String[][] b = new String [m][n];
     
    for (int s = 1; s<m; s++)
    b[s][0] = "";
    for (int z = 1; z<n; z++)
    b[0][z] = "";
     
    for (i = 1; i<m; i++)
    for(j = 1; j<n; j++)
    {
    if(str1.charAt(i-1) == str1.charAt(j-1))
    b[i][j] = b[i-1][j-1]+str1.charAt(+1);
    else if(b[i-1][j].length() >= b[i][j-1].length())
    b[i][j]= b [i-1][j];
    else
      b[i][j] = b[i][j-1];
    }
    return b [m-1][n-1]
    }
    public static void main (String[] args)
    {
    String str1 = "abcs"
    String str2 = "sac"
    System.out.print(find(str1,str2));
    }

    so if you would impliment
    two strings: "abcs" and "sac"
    it should create a matrix that should look like this

    "" "" "" ""
    "" "" "a" "a"
    "" "" "a" "a"
    "" "" "a" "ac"
    "" "s" "s" "ac"

    with the ac as the common between the two
    problem is that Ive tried to run it but doesent get this result
    when i run it.
    can anyone help here?


  2. #2
    Administrator copeg's Avatar
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    Default Re: find LCS

    First, missing a few semi-colons so as is this won't compile. Second,
    if(str1.charAt(i-1) == str1.charAt(j-1))
    I believe you want to compare str1 to str2, not str1 to itself. Next, you should take into account the added first row/column padding for the matrix, so you need to iterate through the matrix taking this into account

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