Added Longest Increasing Subsequence #336

tanyarajhans · 2021-02-27T08:09:56Z

Longest Increasing Subsequence is a famous Dynamic Programming problem which finds out the length of longest increasing subsequence in an array.

This contribution is made as a part of my participation in GirlScript Summer of Code 2021.

codecov · 2021-02-27T15:03:19Z

Codecov Report

Merging #336 (09cf057) into master (a21d00e) will increase coverage by 0.021%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master      #336       +/-   ##
=============================================
+ Coverage   98.550%   98.572%   +0.021%     
=============================================
  Files           25        25               
  Lines         3243      3292       +49     
=============================================
+ Hits          3196      3245       +49     
  Misses          47        47

Impacted Files	Coverage Δ
pydatastructs/linear_data_structures/__init__.py	`100.000% <ø> (ø)`
pydatastructs/linear_data_structures/algorithms.py	`99.629% <100.000%> (+0.031%)`	⬆️
...ucts/miscellaneous_data_structures/disjoint_set.py	`100.000% <0.000%> (ø)`

czgdp1807 · 2021-02-28T05:34:02Z

From now onwards, keep updating this PR for longest increasing sub-sequence.

czgdp1807 · 2021-02-28T05:35:36Z

pydatastructs/linear_data_structures/algorithms.py

+    for i in range(1, n):
+        for j in range(0, i):
+            if seq[i] > seq[j] and lis[i]< lis[j] + 1:
+                lis[i] = lis[j]+1


It is still O(N^2). Please implement O(N log N) version of this algorithm. Update in this PR only. Do not make new PRs.

czgdp1807 · 2021-02-28T05:36:07Z

pydatastructs/linear_data_structures/algorithms.py

@@ -493,12 +449,9 @@ def bucket_sort(array: Array, **kwargs) -> Array:

    References
    ==========
-


Please restore these lines.

tanyarajhans · 2021-02-28T09:38:30Z

Have added nlogn approach for LIS and restored the lines as mentioned before.

czgdp1807 · 2021-02-28T12:29:30Z

pydatastructs/linear_data_structures/algorithms.py

@@ -787,3 +788,65 @@ def longest_common_subsequence(seq1: OneDimensionalArray, seq2: OneDimensionalAr
                    check_mat[i][j] = check_mat[i][j-1]

    return OneDimensionalArray(seq1._dtype, check_mat[row][col][-1])
+
+def longest_increasing_subsequence(seq: OneDimensionalArray) -> int:


The function currently returns only the length. There should be a possibility of obtaining the longest increasing sub-sequence as well.

For example, if ODA([1, 2, -1, 3, 4, 5]) is the input then, (ODA[1, 2, 3, 4, 5], 5) should be the output. Specifically, the first element of the tuple is the LIS and the second is it's length though returning only the sequence will suffice.

Please refer to this for restoring the sequence: https://cp-algorithms.com/sequences/longest_increasing_subsequence.html#toc-tgt-8

czgdp1807 · 2021-02-28T12:31:32Z

pydatastructs/linear_data_structures/algorithms.py

+    tailTable = [0 for i in range(size + 1)]
+    length = 0 # always points empty slot
+
+    tailTable[0] = seq[0]


Use snake case and not camel case.

pydatastructs/utils/tests/test_code_quality.py

czgdp1807 · 2021-02-28T12:32:20Z

Are you editing directly on Github?

Co-authored-by: Gagandeep Singh <gdp.1807@gmail.com>

tanyarajhans · 2021-02-28T12:41:48Z

Are you editing directly on Github?

yeah, just for the last few commits, as CLI wasn't working properly. Will do it from CLI from tomorrow.

Smit-create · 2021-03-09T14:11:14Z

pydatastructs/linear_data_structures/algorithms.py

+    def CeilIndex(A, l, r, key):
+        while (r - l > 1):
+            m = l + (r - l)//2
+            if (A[m] >= key):
+                r = m
+            else:
+                l = m
+        return r


Can we just define and use methods or functions on sorted ODA for finding lower_bound and upper_bound (similar to how it works in cpp)? Instead of defining such private functions?

Can we just define and use methods or functions on sorted ODA for finding lower_bound and upper_bound (similar to how it works in cpp)?

Sure.

Smit-create · 2021-03-10T16:56:52Z

This contribution is made as a part of my participation in GirlScript Summer of Code 2021.

Please provide some updates on the PR or if any difficulty is faced by you so that it can be resolved. As this was stalled for few weeks

Smit-create · 2021-03-13T11:51:50Z

ping @tanyarajhans

tanyarajhans · 2021-03-13T12:42:21Z

ping @tanyarajhans

Hey I am really sorry, for some reason I just received the mail right now. I had exams going on. Will add printing LIS in nlogn in few days, is that fine?

tanyarajhans · 2021-03-13T12:43:47Z

Also, could you please assign this issue to me, as I can see no one is assigned.

Smit-create · 2021-03-15T08:51:02Z

You don't need to worry about the points. As when you will succeed in merging the PR, you will get the assigned points.

sHiVaNgI821 · 2021-03-21T21:07:56Z

I would like to work on this issue as part of my contribution for GSSoC'21. This method would be a part of the algorithms.py file. I would also like to make use of the lower_bound function which I have recently raised a PR for. The time complexity for this method, with the use of the lower_bound function would be O(nlogn).

The function definition goes as follows:-

def longest_increasing_subsequence(array: OneDimensionalArray ) -> OneDimensionalArray : 
        # algo (returns a OneDimensionalArray, which is the longest increasing subsequence
                     for that array)
        return longestIncreasingSubsequence

Smit-create · 2021-03-23T10:34:57Z

Closing in favor of #363

tanyarajhans added 3 commits February 27, 2021 13:21

Added Longest Increasing Subsequence

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Added LIS

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Updated test_algorithms.py

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tanyarajhans force-pushed the demo branch from 86cbb1d to e882023 Compare February 27, 2021 08:21

tanyarajhans added 14 commits February 27, 2021 13:52

Updated __init__.py

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czgdp1807 added algorithms GSSoC linear_data_structures linear_data_structures.algorithms labels Feb 27, 2021

tanyarajhans added 5 commits February 27, 2021 19:57

Fixed errors

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tanyarajhans changed the title ~~Demo~~ Added Longest Increasing Subsequence Feb 27, 2021

czgdp1807 reviewed Feb 28, 2021

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czgdp1807 added the hard label Feb 28, 2021

tanyarajhans added 7 commits February 28, 2021 14:14

Restored lines

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Update algorithms.py

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NlogN approach for LIS

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Indentation fixed

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Update algorithms.py

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Update algorithms.py

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czgdp1807 reviewed Feb 28, 2021

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pydatastructs/utils/tests/test_code_quality.py Outdated Show resolved Hide resolved

Update pydatastructs/utils/tests/test_code_quality.py

09cf057

Co-authored-by: Gagandeep Singh <gdp.1807@gmail.com>

Smit-create reviewed Mar 9, 2021

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tanyarajhans closed this Mar 15, 2021

Smit-create reopened this Mar 16, 2021

Smit-create added the Please take over PRs that can be continued by anyone. label Mar 16, 2021

Smit-create closed this Mar 23, 2021

		@@ -493,12 +449,9 @@ def bucket_sort(array: Array, **kwargs) -> Array:

		References
		==========

Added Longest Increasing Subsequence #336

Added Longest Increasing Subsequence #336

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tanyarajhans commented Feb 27, 2021

Longest Increasing Subsequence is a famous Dynamic Programming problem which finds out the length of longest increasing subsequence in an array.

This contribution is made as a part of my participation in GirlScript Summer of Code 2021.

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