modified: README.md

new file:   tests/linkedList_test.go

README.md

@@ -1,4 +1,4 @@
-# DS
+# Data Structures & Algorithms in Go
 
 ## Linear
 
@@ -8,13 +8,35 @@
 - [ ] Circular Buffer
 - [ ] Deque
 
-## Graph
+## Tree — hierarchical, parent/child relationships
 
-## Tree
+- [ ] Binary Tree
+- [ ] Binary Search Tree
+- [ ] AVL Tree
+- [ ] Heap (min/max)
+- [ ] Trie
+
+## Graph — nodes connected by edges, no strict hierarchy
+
+- [ ] Directed
+- [ ] Undirected
+- [ ] Weighted
+
+## Hash Based — key/value
+
+- [ ] Hash Map
+- [ ] Hash Set
+
+# Each category solves different problems:
+
+- Linear — ordered data, undo/redo, scheduling
+- Tree — searching, sorting, hierarchical data like file systems
+- Graph — networks, maps, social connections, dependencies
+- Hash — fast lookups, caching, counting
+- Set — membership testing, deduplication
 
 # Documentation
 
 ```bash
 go doc -all ./linear | bat -l go
-
 ```

tests/linkedList_test.go

@@ -0,0 +1,260 @@
+package tests
+
+import (
+	"testing"
+
+	"datastructures/linear"
+)
+
+// --- InsertAtHead ---
+
+func TestLinkedListInsertAtHeadSingle(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(42)
+
+	got := ll.Data()
+	if got == nil {
+		t.Fatal("expected non-nil Data after InsertAtHead, got nil")
+	}
+	if *got != 42 {
+		t.Errorf("expected 42, got %d", *got)
+	}
+}
+
+func TestLinkedListInsertAtHeadOrderIsLIFO(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(1)
+	ll.InsertAtHead(2)
+	ll.InsertAtHead(3)
+
+	got := ll.Data()
+	if got == nil || *got != 3 {
+		t.Errorf("expected 3 (last inserted) at head, got %v", got)
+	}
+}
+
+// --- InsertAtTail ---
+
+func TestLinkedListInsertAtTailSingle(t *testing.T) {
+	ll := &linear.LinkedList[string]{}
+	ll.InsertAtTail("hello")
+
+	got := ll.Data()
+	if got == nil || *got != "hello" {
+		t.Errorf("expected 'hello' at head, got %v", got)
+	}
+}
+
+func TestLinkedListInsertAtTailDoesNotMoveHead(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(1)
+	ll.InsertAtTail(2)
+	ll.InsertAtTail(3)
+
+	got := ll.Data()
+	if got == nil || *got != 1 {
+		t.Errorf("expected head to remain 1 after tail inserts, got %v", got)
+	}
+}
+
+// --- Data ---
+
+func TestLinkedListDataOnEmpty(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	if ll.Data() != nil {
+		t.Error("expected nil Data on empty list")
+	}
+}
+
+// --- DeleteHead ---
+
+func TestLinkedListDeleteHeadOnEmpty(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.DeleteHead() // must not panic
+	if ll.Data() != nil {
+		t.Error("expected nil Data after DeleteHead on empty list")
+	}
+}
+
+func TestLinkedListDeleteHeadSingleElement(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(5)
+	ll.DeleteHead()
+
+	if ll.Data() != nil {
+		t.Error("expected nil after deleting the only element via DeleteHead")
+	}
+}
+
+func TestLinkedListDeleteHeadAdvancesHead(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(1)
+	ll.InsertAtHead(2)
+	ll.InsertAtHead(3)
+
+	ll.DeleteHead()
+
+	got := ll.Data()
+	if got == nil || *got != 2 {
+		t.Errorf("expected 2 after deleting head (3), got %v", got)
+	}
+}
+
+// --- DeleteTail ---
+
+func TestLinkedListDeleteTailOnEmpty(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.DeleteTail() // must not panic
+	if ll.Data() != nil {
+		t.Error("expected nil Data after DeleteTail on empty list")
+	}
+}
+
+func TestLinkedListDeleteTailSingleElement(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtTail(10)
+	ll.DeleteTail()
+
+	if ll.Data() != nil {
+		t.Error("expected nil after deleting the only element via DeleteTail")
+	}
+}
+
+func TestLinkedListDeleteTailRemovesLastElement(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtTail(1)
+	ll.InsertAtTail(2)
+	ll.InsertAtTail(3)
+
+	ll.DeleteTail()
+
+	// walk head → next to verify 3 is gone
+	got := ll.Data()
+	if got == nil || *got != 1 {
+		t.Errorf("expected head to remain 1, got %v", got)
+	}
+	ll.DeleteHead()
+	got = ll.Data()
+	if got == nil || *got != 2 {
+		t.Errorf("expected second element to be 2 (3 was deleted), got %v", got)
+	}
+	ll.DeleteHead()
+	if ll.Data() != nil {
+		t.Error("expected empty list after removing all elements")
+	}
+}
+
+// --- string type ---
+
+func TestLinkedListWithStrings(t *testing.T) {
+	ll := &linear.LinkedList[string]{}
+	ll.InsertAtHead("bob")
+	ll.InsertAtHead("alice")
+
+	got := ll.Data()
+	if got == nil || *got != "alice" {
+		t.Errorf("expected alice at head, got %v", got)
+	}
+
+	ll.DeleteHead()
+	got = ll.Data()
+	if got == nil || *got != "bob" {
+		t.Errorf("expected bob after deleting alice, got %v", got)
+	}
+}
+
+func TestLinkedListZeroValue(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(0)
+
+	got := ll.Data()
+	if got == nil || *got != 0 {
+		t.Errorf("expected zero-value int at head, got %v", got)
+	}
+}
+
+// --- pointer type ---
+
+func TestLinkedListWithPointers(t *testing.T) {
+	ll := &linear.LinkedList[*int]{}
+	v1, v2 := 10, 20
+	p1, p2 := &v1, &v2
+
+	ll.InsertAtTail(p1)
+	ll.InsertAtTail(p2)
+
+	got := ll.Data()
+	if got == nil || *got != p1 {
+		t.Errorf("expected p1 at head, got %v", got)
+	}
+}
+
+func TestLinkedListPointerMutation(t *testing.T) {
+	ll := &linear.LinkedList[*int]{}
+	v := 42
+	p := &v
+	ll.InsertAtHead(p)
+
+	v = 99
+
+	got := ll.Data()
+	if got == nil || **got != 99 {
+		t.Errorf("expected mutation reflected via pointer, got %v", got)
+	}
+}
+
+func TestLinkedListNilPointer(t *testing.T) {
+	ll := &linear.LinkedList[*int]{}
+	ll.InsertAtHead(nil)
+
+	got := ll.Data()
+	if got == nil {
+		t.Fatal("expected non-nil Data pointer (pointing to a nil *int), got nil")
+	}
+	if *got != nil {
+		t.Errorf("expected stored nil *int, got %v", *got)
+	}
+}
+
+// --- mixed operations ---
+
+func TestLinkedListAlternatingInsertDelete(t *testing.T) {
+	ll := &linear.LinkedList[int]{}
+	ll.InsertAtHead(1)
+	ll.InsertAtTail(2)
+	ll.InsertAtHead(0)
+	// list: 0 <--> 1 <--> 2
+
+	ll.DeleteTail()
+	// list: 0 <--> 1
+
+	got := ll.Data()
+	if got == nil || *got != 0 {
+		t.Errorf("expected 0 at head, got %v", got)
+	}
+
+	ll.DeleteHead()
+	// list: 1
+	got = ll.Data()
+	if got == nil || *got != 1 {
+		t.Errorf("expected 1 as sole remaining element, got %v", got)
+	}
+
+	ll.DeleteHead()
+	if ll.Data() != nil {
+		t.Error("expected empty list after deleting all elements")
+	}
+}
+
+func TestLinkedListDeleteBothEndsToEmpty(t *testing.T) {
+	ll := &linear.LinkedList[string]{}
+	ll.InsertAtTail("a")
+	ll.InsertAtTail("b")
+
+	ll.DeleteHead()
+	ll.DeleteTail()
+
+	if ll.Data() != nil {
+		t.Error("expected empty list after removing both elements")
+	}
+}