Adding Longest Common Subsequence #315

Arvind-raj06 · 2021-01-16T14:40:03Z

Longest Common Subsequence

References to other Issues or PRs or Relevant literature

"Fixes #308". See
#308

Brief description of what is fixed or changed

The Longest Common Subsequence algorithm is added in the linear data structure with reference to the site https://www.geeksforgeeks.org/longest-common-subsequence-dp-4/

Other comments

Hope this works fine and if there is any issue please ping me. This is also part of SWoC contribution

sidhu1012 · 2021-01-16T16:33:32Z

pydatastructs/linear_data_structures/algorithms.py

+
+    .. [1] https://en.wikipedia.org/wiki/Longest_common_subsequence_problem
+    """
+    if not(isinstance(seq1, (str, tuple, list))) or not(isinstance(seq2, (str, tuple, list))):


Break it into two. As did earlier.

Yep are there any changes needed

sidhu1012 · 2021-01-16T17:01:31Z

pydatastructs/linear_data_structures/algorithms.py

+    """
+    if not(isinstance(seq1, (str, tuple, list))):


A blank line after 759 and it isn't necessary to use brackets with not.
It should be
if not isinstance (...)

Can you just find all the issue and report me, as Gagandeep asked me to reduce the commits to reduce the resource used by travis

I will change this for now.

Can you just find all the issue and report me, as Gagandeep asked me to reduce the commits to reduce the resource used by travis

Issues can only be reported when they arise. Can't report them before their occurance.

Commits can be squashed into one so no worries.

sidhu1012

LGTM!

sidhu1012 · 2021-01-16T17:23:10Z

Squash commits if necessary.
Ping @czgdp1807

sidhu1012 · 2021-01-17T01:52:48Z

pydatastructs/linear_data_structures/tests/test_algorithms.py

+    I, J = ['O', 'V', 'A', 'L'], ['F', 'O', 'R', 'V', 'A', 'E', 'W']
+    output = longest_common_subsequence(I, J)
+    assert expected_result == output


Add one test case for tuple too.

Yeah sure that can be done

czgdp1807 · 2021-01-17T05:50:02Z

pydatastructs/linear_data_structures/algorithms.py

+    seq1: String or List or Tuple
+    seq2: String or List or Tuple


Suggested change

seq1: String or List or Tuple

seq2: String or List or Tuple

seq1: Any 1D data structure that can be indexed (like list, tuple, string)

seq2: Any 1D data structure that can be indexed (like list, tuple, string)

czgdp1807 · 2021-01-17T05:52:44Z

pydatastructs/linear_data_structures/algorithms.py

+    output: tuple
+    (Length of LCS, Common Sequence)
+    Common Sequence will be of the same data type as seq1.


Suggested change

output: tuple

(Length of LCS, Common Sequence)

Common Sequence will be of the same data type as seq1.

output: tuple

The first element of the tuple represents the length of longest common subsequence and

the second element is the longest common subsequence itself.

Common subsequence will be of the same data type as that of input sequences.

czgdp1807 · 2021-01-17T05:53:04Z

pydatastructs/linear_data_structures/algorithms.py

+    if not isinstance(seq1, (str, tuple, list)):
+        raise TypeError("Only Strings, Tuple and List are allowed")
+    if not isinstance(seq2, (str, tuple, list)):
+        raise TypeError("Only Strings, Tuple and List are allowed")


Suggested change

if not isinstance(seq1, (str, tuple, list)):

raise TypeError("Only Strings, Tuple and List are allowed")

if not isinstance(seq2, (str, tuple, list)):

raise TypeError("Only Strings, Tuple and List are allowed")

czgdp1807 · 2021-01-17T05:59:15Z

pydatastructs/linear_data_structures/algorithms.py

+        raise TypeError("Only Strings, Tuple and List are allowed")
+
+    row, col = len(seq1), len(seq2)
+    check_mat = [[0 for _ in range(col+1)] for x in range(row+1)]


What about using a nested dict. AFAICT, half of the matrix in these type of problems is untouched and wasted. dict will be at least theoretically better.

Arvind-raj06 · 2021-01-17T13:22:58Z

 for i in range(row):
    check_mat[i+1]=[0 for _ in range(col+1)]
    for j in range(col):
           if (seq1[i] == seq2[j]):
                check_mat[i+1][j+1] = check_mat[i][j]+1
            else:
                check_mat[i+1][j+1] = max(check_mat[i+1][j], check_mat[i][j+1])

I tried it in nested dict but at the else part in comparison had the index not present in dictionary. So I had to implement them in list within dictionary

czgdp1807 · 2021-01-18T06:26:15Z

pydatastructs/linear_data_structures/algorithms.py

+    if(type(seq1) == str):
+        lcseq = ''.join(lcseq)
+    if(type(seq1) == tuple):
+        lcseq = tuple(lcseq)
+    return (lclen, lcseq[::-1])


This part is cryptic. We should keep the input types restricted to OneDimensionalArray only, otherwise such things will create problems while porting the code to statically typed languages like C++.
In addition, applying longest common subseqeunce on strings would be confusing because there is already something called longest common substring.
Hence the final API should be, accept two OneDimensionalArray objects and return a OneDimensionalArray.

P.S. That is why doing some background lookups are preferred for discussing APIs rather than just directly coding out things and keep changing frequently.

Yeah next time onwards we discuss and start the implementation and I will try to implement the above in One dimensional

czgdp1807 · 2021-01-18T06:26:58Z

See, https://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Code_optimization and include the ideas in the page in your code.

Arvind-raj06 · 2021-01-18T08:02:33Z

See, https://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Code_optimization and include the ideas in the page in your code.

Yeah got that

Arvind-raj06 · 2021-01-19T07:06:59Z

If I had to implement them as in the Wikipedia, the left out comparison had to be added manually that would look cryptic. But still the comparison time complexity is reduced rather than before and for space complexity if I reduce them the time gets increased as it has to be in recursive.

You can preview it here in the implementation

Arvind-raj06 · 2021-01-19T07:12:37Z

@czgdp1807 Label for the Swoc and be attached here and also for the #312 for making the counting easier

Arvind-raj06 added 30 commits January 7, 2021 10:58

Update queue.py

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Update linked_lists.py

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Update linked_lists.py

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Completed updating the insert_after

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Update linked_lists.py

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Update queue.py

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Update linked_lists.py

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Cocktail

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Update algorithms.py

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Implementing the cocktail sort

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Update __init__.py

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Correcting error

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Completion

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Converting to ODA

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Update algorithms.py

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Update algorithms.py

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Really!

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Including cocktail sort

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Correcting for doda

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Error Correction

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Yep done!

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Hope this works fine

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Update algorithms.py

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Commit

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Update algorithms.py

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sidhu1012 reviewed Jan 16, 2021

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Yes added

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czgdp1807 mentioned this pull request Jan 17, 2021

[WIP] Added Longest Common Sequence #310

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czgdp1807 added linear_data_structures linear_data_structures.algorithms labels Jan 17, 2021

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czgdp1807 added 2 commits January 19, 2021 13:14

Added tests and fixed docs

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fixed docs

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czgdp1807 merged commit 4e0372d into codezonediitj:master Jan 19, 2021

Arvind-raj06 deleted the Don'tstop branch January 23, 2021 09:58

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Adding Longest Common Subsequence #315

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Adding Longest Common Subsequence #315

Adding Longest Common Subsequence #315

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Arvind-raj06 commented Jan 16, 2021 • edited Loading

Longest Common Subsequence

References to other Issues or PRs or Relevant literature

Brief description of what is fixed or changed

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