Solve Data Structure by yonieas · Pull Request #2 · josestg/dsa

yonieas · 2026-02-10T09:18:56Z

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Copilot

Pull request overview

This PR implements core functionality for multiple data structures including Binary Search Tree, Stack, Queue, HashSet, HashMap, Graph, and various LinkedList implementations. The implementation replaces panic("todo: please implement me!") stubs with working code for operations like insertion, deletion, traversal, and searching across all these data structures.

Changes:

Implemented BST operations (Add, Del, Exists, Min, Max) with tree traversal methods (InOrder, PreOrder, PostOrder)
Implemented Stack and Queue operations with backend initialization
Implemented HashSet operations (Add, Del, Union, Intersection, Disjoint) and HashMap operations (Put, Del, Get, rehashing)
Implemented Graph operations (AddEdge, DelEdge, HasEdge, vertex iteration)
Implemented LinkedList operations for Singly, Doubly, and Circular variants (Append, Prepend, Pop, Shift, Insert, Remove)
Implemented DynamicArray operations with automatic resizing
Implemented BitSet operations for set manipulation
Updated CI workflow to include "master" branch

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
tree/binary_search_tree.go	Implements BST insertion, deletion, search, and traversal operations using recursive helpers
stack/stack.go	Implements stack operations with backend initialization and delegation to linked list
sets/hashset.go	Implements set operations including union, intersection, and disjoint checks using hashmap backend
queue/queue.go	Implements queue operations with backend initialization and delegation to linked list
linkedlist/singly_linkedlist.go	Implements singly linked list operations including insertion, deletion, and traversal
linkedlist/doubly_linkedlist.go	Implements doubly linked list operations with bidirectional traversal and optimized node finding
linkedlist/circular_doubly_linkedlist.go	Implements circular doubly linked list operations maintaining circular structure
hashmap/hashmap_chaining.go	Implements hash map with chaining collision resolution, including dynamic resizing
graph/graph.go	Implements graph operations using adjacency list representation for both directed and undirected graphs
dynamicarray/dynamicarray.go	Implements dynamic array with automatic capacity doubling and element manipulation
dynamicarray/dynamicarray_test.go	Adds EnumBackward test case
bitsets/bitsets.go	Implements bitset operations for efficient integer set representation
.github/workflows/ci.yml	Updates CI to trigger on both "master" and "main" branches

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Copilot · 2026-02-13T08:29:45Z

+				for i, v := range sequence.Enum(list.Iter) {
+					if v == from {
+						list.Remove(i)
+					}


The same logic error exists here: after removing an edge with list.Remove(i), the loop continues without a break statement. This can cause incorrect behavior if there are multiple edges or lead to index errors. Add a break statement after list.Remove(i).

Copilot · 2026-02-13T08:29:45Z

+	d.Append(value)
+	for i := d.size - 1; i > 0; i-- {
+		d.Swap(i, i-1)
+	}
+	d.backend.Set(0, value)
+	// d.size++


The Prepend method has inefficient logic. It calls Append(value) first which adds the value to the end and increments size, then swaps elements to move it to the front, but never decrements size. This means size is incorrectly incremented twice. The commented line "// d.size++" at line 301 confirms this issue. Instead of using Append, the implementation should check capacity, grow if needed, shift elements right, set value at index 0, and increment size once.

Suggested change

d.Append(value)

for i := d.size - 1; i > 0; i-- {

d.Swap(i, i-1)

}

d.backend.Set(0, value)

// d.size++

// Place the new value at the new logical end, then move it to the front.

d.backend.Set(d.size, value)

d.size++

for i := d.size - 1; i > 0; i-- {

d.Swap(i, i-1)

}

Copilot · 2026-02-13T08:29:45Z

+	result := New(b.Len())
+	for i, _ := range result.bitfields {


The Disjoint method unnecessarily creates a new BitSet result but never uses it for the intended purpose. The result variable is initialized but only used to determine loop range. The variable should be removed as it wastes memory and serves no purpose in the logic.

Suggested change

result := New(b.Len())

for i, _ := range result.bitfields {

for i := range b.bitfields {

Copilot · 2026-02-13T08:29:46Z

+		panic("BitSets.Union: The length unmatch")
+	}
+	result := New(b.Len())
+	for i, _ := range result.bitfields {


Blank identifier should not be used in range loops when the value is not needed. Change "for i, _ := range result.bitfields" to "for i := range result.bitfields"

Suggested change

for i, _ := range result.bitfields {

for i := range result.bitfields {

Copilot · 2026-02-13T08:29:46Z

+		panic("BitSets.Intersection: The length unmatch")
+	}
+	result := New(b.Len())
+	for i, _ := range result.bitfields {


Blank identifier should not be used in range loops when the value is not needed. Change "for i, _ := range result.bitfields" to "for i := range result.bitfields"

Copilot · 2026-02-13T08:29:46Z

+		for i, v := range sequence.Enum(list.Iter) {
+			if v == to {
+				list.Remove(i)
+			}


The DelEdge method has a logic error: it removes all edges from 'from' to 'to', but the break statement is missing after list.Remove(i). Without a break, the iteration continues with incorrect indices after removal, and may remove multiple edges or cause index errors. Add a break statement after list.Remove(i) to exit the loop once the edge is found and removed.

Copilot · 2026-02-13T08:29:47Z

+		return shiftData, true
+	} else {
+		tail := l.head.prev
+		newHead := l.head.next


The TryShift method in CircularDoublyLinkedList doesn't properly rewire tail.next when removing the head in a multi-node list. After setting newHead and newHead.prev = tail, the code should also set tail.next = newHead to maintain the circular structure. Currently, tail still points to the old (removed) head.

Suggested change

newHead := l.head.next

newHead := l.head.next

tail.next = newHead

Copilot · 2026-02-13T08:29:47Z

 	// hint: if s.b == nil, initialize it with linkedlist.NewDoublyLinkedList[E]()
-	panic("todo: please implement me!")
+	if s.b == nil {
+		linkedlist.NewDoublyLinkedList[E]()


The ensureBackend function creates a new backend but doesn't assign it to s.b. The created backend is immediately discarded, so s.b remains nil. This will cause all stack operations to fail. The assignment should be: s.b = linkedlist.NewDoublyLinkedListE

Suggested change

linkedlist.NewDoublyLinkedList[E]()

s.b = linkedlist.NewDoublyLinkedList[E]()

Copilot · 2026-02-13T08:29:47Z

+		// Have two children
+		successor, _ := t.Min()


In the deleteHelper method for a node with two children, the code incorrectly calls t.Min() to find the successor. This returns the minimum value of the entire tree (from the root), not the minimum value in the right subtree of the node being deleted. The correct approach is to find the minimum node in node.right's subtree. Consider adding a helper method that finds the minimum starting from a given node, or traverse node.right to its leftmost descendant.

Suggested change

// Have two children

successor, _ := t.Min()

// Have two children: find the minimum in the right subtree (successor)

successorNode := node.right

for successorNode.left != nil {

successorNode = successorNode.left

}

successor := successorNode.data

Copilot · 2026-02-13T08:29:47Z

+	return t.existsHelper(t.root, value)
+}
+
+// Recursive helper for `Exist` method


The comment refers to 'Exist' method, but the actual method name is 'Exists'. The comment should say "Recursive helper for Exists method"

Suggested change

// Recursive helper for `Exist` method

// Recursive helper for `Exists` method

yonieas added 18 commits January 28, 2026 14:38

fix: solve dynamic array

be505c5

test: add EnumBackward prop

c03f8aa

fix: solve single linkedlist

3703bd6

update: change CI to master

3d77ebb

Merge branch 'dev'

b5a5253

fix: solve double linkedlist

f0025bc

fix: solve circular doubly linkedlist

9bca87d

Merge branch 'dev'

7c2d852

fix: solve Stack

88f5fe4

fix: solve Queue

eb32f16

fix: solve Hashmap

ecfe9e0

fix: solve HashSet

3550d94

fix: solve Graph

33b1d4f

fix: solve Tree

85e8298

fix: solve Bitset

43112d3

chore: clean the panic comment

85f0186

Merge branch 'dev'

c1e63d3

update: add branch main again

44ceae0

josestg requested a review from Copilot February 13, 2026 08:26

Copilot started reviewing on behalf of josestg February 13, 2026 08:27 View session

Copilot AI reviewed Feb 13, 2026

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Solve Data Structure#2

Solve Data Structure#2
yonieas wants to merge 18 commits into
josestg:mainfrom
yonieas:master

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	result := New(b.Len())
	for i, _ := range result.bitfields {
	for i := range b.bitfields {

	for i, _ := range result.bitfields {
	for i := range result.bitfields {

	newHead := l.head.next
	newHead := l.head.next
	tail.next = newHead

	linkedlist.NewDoublyLinkedList[E]()
	s.b = linkedlist.NewDoublyLinkedList[E]()

-		// Have two children
-		successor, _ := t.Min()
+		// Have two children: find the minimum in the right subtree (successor)
+		successorNode := node.right
+		for successorNode.left != nil {
+			successorNode = successorNode.left
+		}
+		successor := successorNode.data

	// Recursive helper for `Exist` method
	// Recursive helper for `Exists` method

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