Package org.eclipse.compare.internal

Class LCS

java.lang.Object
org.eclipse.compare.internal.LCS
Direct Known Subclasses:
RangeComparatorLCS
public abstract class LCS extends Object

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private int
    length
     
    private int
    max_differences
     

  • Constructor Summary

    Constructors
    Constructor
    Description
    LCS()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    private int
    find_middle_snake(int bottoml1, int topl1, int bottoml2, int topl2, int[][] V, int[] snake)
    Helper function for Myers' LCS algorithm to find the middle snake for l1[bottoml1..topl1] and l2[bottoml2..topl2] The x, y coodrdinates of the start of the middle snake are saved in snake[0], snake[1] respectively and the length of the snake is saved in s[2].
    private static int[]
    findMostProgress(int M, int N, int limit, int[][] V)
    Takes the array with furthest reaching D-paths from an LCS computation and returns the x,y coordinates and progress made in the middle diagonal among those with maximum progress, both from the front and from the back.
    int
    getLength()
     
    protected abstract int
    getLength1()
     
    protected abstract int
    getLength2()
     
    protected abstract void
    initializeLcs(int lcsLength)
     
    protected abstract boolean
    isRangeEqual(int i1, int i2)
     
    private int
    lcs_rec(int bottoml1, int topl1, int bottoml2, int topl2, int[][] V, int[] snake)
    The recursive helper function for Myers' LCS.
    void
    longestCommonSubsequence(LCSSettings settings)
    Myers' algorithm for longest common subsequence.
    protected abstract void
    setLcs(int sl1, int sl2)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • max_differences

      private int max_differences

    • length

      private int length

  • Constructor Details

    • LCS

      public LCS()

  • Method Details

    • longestCommonSubsequence

      public void longestCommonSubsequence(LCSSettings settings)
      Myers' algorithm for longest common subsequence. O((M + N)D) worst case time, O(M + N + D^2) expected time, O(M + N) space (http://citeseer.ist.psu.edu/myers86ond.html) Note: Beyond implementing the algorithm as described in the paper I have added diagonal range compression which helps when finding the LCS of a very long and a very short sequence, also bound the running time to (N + M)^1.5 when both sequences are very long. After this method is called, the longest common subsequence is available by calling getResult() where result[0] is composed of entries from l1 and result[1] is composed of entries from l2
      Parameters:
      subMonitor -

    • lcs_rec

      private int lcs_rec(int bottoml1, int topl1, int bottoml2, int topl2, int[][] V, int[] snake)
      The recursive helper function for Myers' LCS. Computes the LCS of l1[bottoml1 .. topl1] and l2[bottoml2 .. topl2] fills in the appropriate location in lcs and returns the length
      Parameters:
      l1 - The 1st sequence
      bottoml1 - Index in the 1st sequence to start from (inclusive)
      topl1 - Index in the 1st sequence to end on (inclusive)
      l2 - The 2nd sequence
      bottoml2 - Index in the 2nd sequence to start from (inclusive)
      topl2 - Index in the 2nd sequence to end on (inclusive)
      V - should be allocated as int[2][l1.length + l2.length + 1], used to store furthest reaching D-paths
      snake - should be allocated as int[3], used to store the beginning x, y coordinates and the length of the latest snake traversed
      subMonitor -
      lcs - should be allocated as TextLine[2][l1.length], used to store the common points found to be part of the LCS where lcs[0] references lines of l1 and lcs[1] references lines of l2.
      Returns:
      the length of the LCS

    • find_middle_snake

      private int find_middle_snake(int bottoml1, int topl1, int bottoml2, int topl2, int[][] V, int[] snake)
      Helper function for Myers' LCS algorithm to find the middle snake for l1[bottoml1..topl1] and l2[bottoml2..topl2] The x, y coodrdinates of the start of the middle snake are saved in snake[0], snake[1] respectively and the length of the snake is saved in s[2].
      Parameters:
      l1 - The 1st sequence
      bottoml1 - Index in the 1st sequence to start from (inclusive)
      topl1 - Index in the 1st sequence to end on (inclusive)
      l2 - The 2nd sequence
      bottoml2 - Index in the 2nd sequence to start from (inclusive)
      topl2 - Index in the 2nd sequence to end on (inclusive)
      V - should be allocated as int[2][l1.length + l2.length + 1], used to store furthest reaching D-paths
      snake - should be allocated as int[3], used to store the beginning x, y coordinates and the length of the middle snake
      Returns:
      The number of differences (SES) between l1[bottoml1..topl1] and l2[bottoml2..topl2]

    • findMostProgress

      private static int[] findMostProgress(int M, int N, int limit, int[][] V)
      Takes the array with furthest reaching D-paths from an LCS computation and returns the x,y coordinates and progress made in the middle diagonal among those with maximum progress, both from the front and from the back.
      Parameters:
      M - the length of the 1st sequence for which LCS is being computed
      N - the length of the 2nd sequence for which LCS is being computed
      limit - the number of steps made in an attempt to find the LCS from the front and back
      V - the array storing the furthest reaching D-paths for the LCS computation
      Returns:
      The result as an array of 3 integers where result[0] is the x coordinate of the current location in the diagonal with the most progress, result[1] is the y coordinate of the current location in the diagonal with the most progress and result[2] is the amount of progress made in that diagonal

    • getLength2

      protected abstract int getLength2()

    • getLength1

      protected abstract int getLength1()

    • isRangeEqual

      protected abstract boolean isRangeEqual(int i1, int i2)

    • setLcs

      protected abstract void setLcs(int sl1, int sl2)

    • initializeLcs

      protected abstract void initializeLcs(int lcsLength)

    • getLength

      public int getLength()