Data Structures in Go

12 essential data structures for Go developers. Each one explained with Big O complexity, animated visuals, and real code samples you can copy.

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ArrayDynamic ArrayStackQueueHash MapHash SetLinked ListSorted Set (BST)Sorted Map (BST)Priority Queue (Heap)Concurrent Hash MapMemory View / Slice

Array

[n]T

Fixed-size, contiguous block of memory. Elements are stored sequentially and accessed by index in constant time. The foundation of most other data structures.

7
3
9
1
5
[0]
[1]
[2]
[3]
[4]

arr[0] = 7

Complexity

Access by indexO(1)
SearchO(n)
Insert / DeleteO(n)

When to use

  • +You know the exact size at creation time
  • +You need the fastest possible index-based access
  • +Working with fixed-length data like matrices or buffers
Go
// Arrays are fixed-size, value types (copied on assignment)
var nums [5]int                  // zero-valued: [0,0,0,0,0]
primes := [5]int{2, 3, 5, 7, 11}

primes[0] = 13                   // O(1) access
third := primes[2]               // O(1) -> 5

// Length is part of the type - [5]int != [3]int
fmt.Println(len(primes))         // 5

// Iterate
for i, v := range primes {
    fmt.Printf("index %d: %d\n", i, v)
}

// Arrays are rarely used directly - slices are preferred
// Comparison: arrays support == (slices do not)
fmt.Println(nums == [5]int{})    // true

Dynamic Array

[]T (slice)

Resizable array that automatically grows when capacity is exceeded. The most commonly used data structure in most languages. Doubles its internal storage when full, giving amortized O(1) appends.

7
3
9
1
5
[0]
[1]
[2]
[3]
[4]

arr[0] = 7

Complexity

Access by indexO(1)
SearchO(n)
AppendO(1)*
Insert / Remove (middle)O(n)

When to use

  • +You need a resizable collection (most common case)
  • +You frequently access elements by index
  • +You mostly add or remove at the end
Go
// Slices are Go's dynamic array (backed by an array)
nums := []int{10, 20, 30}

nums = append(nums, 40)          // O(1) amortized
nums = append(nums, 50)          // doubles cap when full

nums[1] = 25                     // O(1) index access

// Insert at index 2 - O(n)
nums = slices.Insert(nums, 2, 28)

// Delete at index 1 - O(n)
nums = slices.Delete(nums, 1, 2)

// Search
idx := slices.Index(nums, 40)    // O(n)
has := slices.Contains(nums, 28) // O(n)

// Sort
slices.Sort(nums)                // O(n log n)
fmt.Println(nums, len(nums), cap(nums))

Stack

[]T (slice)

Last-In-First-Out (LIFO) collection. Only the top element is accessible. Used for tracking state that must be unwound in reverse order.

arrow_downward top
10

Push 10

Complexity

PushO(1)
PopO(1)
PeekO(1)
SearchO(n)

When to use

  • +Undo/redo functionality
  • +Expression parsing and evaluation
  • +DFS traversal of trees and graphs
  • +Matching brackets, parentheses validation
Go
// Use a slice as a stack (LIFO)
stack := []int{}

// Push - O(1) amortized
stack = append(stack, 10)
stack = append(stack, 20)
stack = append(stack, 30)

// Peek - O(1)
top := stack[len(stack)-1]       // 30

// Pop - O(1)
stack = stack[:len(stack)-1]     // [10, 20]

// Interview pattern: valid parentheses
func isValid(s string) bool {
    st := []rune{}
    pairs := map[rune]rune{')': '(', ']': '[', '}': '{'}
    for _, c := range s {
        if p, ok := pairs[c]; ok {
            if len(st) == 0 || st[len(st)-1] != p { return false }
            st = st[:len(st)-1]
        } else { st = append(st, c) }
    }
    return len(st) == 0
}

Queue

container/list

First-In-First-Out (FIFO) collection. Elements are added at the back and removed from the front. Fundamental for breadth-first processing.

front
10
back

Enqueue 10

Complexity

EnqueueO(1)
DequeueO(1)
PeekO(1)
SearchO(n)

When to use

  • +BFS traversal of trees and graphs
  • +Task scheduling and job queues
  • +Message passing between components
  • +Rate limiting, buffering
Go
// Slice-based queue (simple, fine for interviews)
queue := []string{}

queue = append(queue, "A")        // O(1) enqueue
queue = append(queue, "B")
queue = append(queue, "C")

front := queue[0]                 // O(1) peek -> "A"
queue = queue[1:]                 // O(1)* dequeue (re-slicing)

// For production, use container/list (doubly-linked)
import "container/list"
q := list.New()
q.PushBack("task1")              // O(1) enqueue
q.PushBack("task2")
elem := q.Front()                // O(1) peek
q.Remove(elem)                   // O(1) dequeue

// Or use a channel as a bounded queue
ch := make(chan int, 100)
ch <- 42                         // enqueue (blocks if full)
val := <-ch                      // dequeue (blocks if empty)

Hash Map

map[K]V

Maps keys to values using a hash function for near-constant-time lookups. The single most important data structure for coding interviews. Every language has a built-in implementation.

0
age:30
1
2
name:Al
3
city:NY

hash("age") = 0

Complexity

InsertO(1)*
LookupO(1)
DeleteO(1)
Contains keyO(1)

When to use

  • +Two Sum and frequency counting patterns
  • +Caching computed results (memoization)
  • +Grouping data by a key
  • +Any problem requiring O(1) lookup by key
Go
// map[K]V - built-in hash map
m := map[string]int{
    "apple":  3,
    "banana": 5,
}

m["cherry"] = 2                    // O(1) add
m["apple"] = 10                    // O(1) update
delete(m, "cherry")                // O(1)

// Safe lookup (comma-ok idiom)
val, ok := m["banana"]             // O(1)
if ok { fmt.Println(val) }        // 5

// Interview pattern: Two Sum
func twoSum(nums []int, target int) [2]int {
    seen := map[int]int{}
    for i, n := range nums {
        need := target - n
        if j, ok := seen[need]; ok {
            return [2]int{j, i}
        }
        seen[n] = i
    }
    return [2]int{-1, -1}
}

Hash Set

map[T]struct{}

Unordered collection of unique elements. Uses hashing internally for O(1) membership testing. Supports mathematical set operations like union, intersection, and difference.

0
age:30
1
2
name:Al
3
city:NY

hash("age") = 0

Complexity

AddO(1)*
ContainsO(1)
RemoveO(1)
Union / IntersectO(n)

When to use

  • +Checking if an element exists in O(1)
  • +Removing duplicates from a collection
  • +Set operations: union, intersection, difference
  • +Visited tracking in graph traversal
Go
// map[T]struct{} - idiomatic set (zero-byte values)
set := map[int]struct{}{
    1: {}, 2: {}, 3: {}, 4: {}, 5: {},
}

set[6] = struct{}{}                // O(1) add
delete(set, 1)                     // O(1) remove

// Check membership
_, has := set[4]                   // O(1) -> true

// Union
other := map[int]struct{}{4: {}, 5: {}, 6: {}, 7: {}}
union := maps.Clone(set)
for k := range other { union[k] = struct{}{} }

// Intersection
inter := map[int]struct{}{}
for k := range set {
    if _, ok := other[k]; ok { inter[k] = struct{}{} }
}

// Interview pattern: contains duplicate
func hasDup(nums []int) bool {
    s := map[int]struct{}{}
    for _, n := range nums { if _, ok := s[n]; ok { return true }; s[n] = struct{}{} }
    return false
}

Linked List

container/list

Sequence of nodes where each node points to the next (singly linked) or both next and previous (doubly linked). Efficient insertion and deletion at any known position, but no index-based access.

5
12
8
20

traversing: 5

Complexity

Insert at head/tailO(1)
Remove (given node)O(1)
SearchO(n)
Access by indexO(n)

When to use

  • +Frequent insertion/deletion in the middle
  • +Implementing LRU cache (with a hash map)
  • +When you need a deque (double-ended queue)
  • +Problems involving pointer manipulation
Go
// container/list - doubly linked list
import "container/list"

ll := list.New()
ll.PushBack(10)                   // O(1) append
ll.PushBack(20)
ll.PushFront(5)                   // O(1) prepend

// Find and insert before - O(n) search, O(1) insert
for e := ll.Front(); e != nil; e = e.Next() {
    if e.Value.(int) == 20 {
        ll.InsertBefore(15, e)    // O(1) given element
        break
    }
}

// Remove - O(1) given element reference
ll.Remove(ll.Front())

// Iterate: 10 -> 15 -> 20
for e := ll.Front(); e != nil; e = e.Next() {
    fmt.Print(e.Value, " ")
}

Sorted Set (BST)

sorted slice

Collection of unique elements maintained in sorted order, typically backed by a balanced binary search tree (red-black tree). Supports range queries and O(log n) min/max.

831215

search(8)

Complexity

AddO(log n)
ContainsO(log n)
RemoveO(log n)
Min / MaxO(log n)

When to use

  • +Maintaining a sorted collection of unique items
  • +Range queries (all elements between X and Y)
  • +Sliding window problems needing sorted order
  • +Leaderboards, ranking systems
Go
// No built-in sorted set - use sorted slice + sort.Search
import "slices"

sorted := []int{1, 3, 5, 8, 9}

// Binary search - O(log n)
idx, found := slices.BinarySearch(sorted, 5)
fmt.Println(idx, found)          // 2, true

// Insert maintaining order - O(n) for shift
pos, _ := slices.BinarySearch(sorted, 4)
sorted = slices.Insert(sorted, pos, 4)
// [1, 3, 4, 5, 8, 9]

min := sorted[0]                 // O(1) -> 1
max := sorted[len(sorted)-1]    // O(1) -> 9

// For O(log n) insert/delete, use a third-party
// red-black tree (e.g., github.com/emirpasic/gods)

Sorted Map (BST)

sorted slice of pairs

Key-value pairs maintained in sorted key order, typically backed by a balanced BST. Enables ordered iteration and range lookups that hash maps cannot provide.

831215

search(8)

Complexity

InsertO(log n)
LookupO(log n)
RemoveO(log n)
Iterate (sorted)O(n)

When to use

  • +You need sorted key-value pairs
  • +Ordered iteration over entries
  • +Range lookups by key
  • +When insertion order or sorted order matters
Go
// No built-in sorted map - sort keys manually
m := map[string]int{
    "banana": 2,
    "apple":  5,
    "cherry": 1,
}

// Collect and sort keys - O(n log n)
keys := make([]string, 0, len(m))
for k := range m {
    keys = append(keys, k)
}
slices.Sort(keys)

// Iterate in sorted order
for _, k := range keys {
    fmt.Printf("%s: %d\n", k, m[k])
}
// apple: 5, banana: 2, cherry: 1

// For O(log n) sorted map, use a third-party btree
// e.g., github.com/google/btree

Priority Queue (Heap)

container/heap

Collection where elements are dequeued by priority rather than insertion order. Typically implemented as a binary heap. Essential for shortest-path algorithms and top-K problems.

13579

min-heap

Complexity

InsertO(log n)
Extract min/maxO(log n)
PeekO(1)
SearchO(n)

When to use

  • +Dijkstra's shortest path algorithm
  • +Merge K sorted lists/streams
  • +Top-K / Kth largest element problems
  • +Event-driven simulation, scheduling
Go
// container/heap - implement heap.Interface
import "container/heap"

type IntHeap []int
func (h IntHeap) Len() int            { return len(h) }
func (h IntHeap) Less(i, j int) bool  { return h[i] < h[j] } // min-heap
func (h IntHeap) Swap(i, j int)       { h[i], h[j] = h[j], h[i] }
func (h *IntHeap) Push(x any)         { *h = append(*h, x.(int)) }
func (h *IntHeap) Pop() any {
    old := *h; n := len(old)
    val := old[n-1]; *h = old[:n-1]
    return val
}

// Usage
h := &IntHeap{5, 3, 8, 1}
heap.Init(h)                      // O(n)
heap.Push(h, 2)                   // O(log n)
min := heap.Pop(h)                // O(log n) -> 1
top := (*h)[0]                    // O(1) peek

Concurrent Hash Map

sync.Map

Thread-safe hash map designed for concurrent read/write access from multiple threads. Uses fine-grained locking or lock-free techniques instead of a single global lock.

0
age:30
1
2
name:Al
3
city:NY

hash("age") = 0

Complexity

InsertO(1)*
LookupO(1)
DeleteO(1)
Atomic updateO(1)*

When to use

  • +Multi-threaded caching
  • +Shared state across threads or async tasks
  • +Producer-consumer patterns with keyed data
  • +When you need concurrent reads and writes
Go
// sync.Map - concurrent-safe map (no generics)
import "sync"

var m sync.Map

m.Store("hits", 0)                // O(1) thread-safe write
val, ok := m.Load("hits")        // O(1) thread-safe read
if ok { fmt.Println(val) }

// LoadOrStore - atomic get-or-set
actual, loaded := m.LoadOrStore("sessions", 1)

// Range over all entries (snapshot)
m.Range(func(key, value any) bool {
    fmt.Printf("%s: %v\n", key, value)
    return true // continue iteration
})

// Delete
m.Delete("hits")                  // O(1)

// For typed concurrent maps, use mutex + map[K]V
// sync.Map is best for read-heavy, stable-key workloads

Memory View / Slice

[]T (slice)

Zero-copy view over a contiguous region of memory. Lets you reference a portion of an array or buffer without allocating new memory. Critical for performance-sensitive parsing and processing.

1
2
3
4
5
6

Span[0..3] = [1, 2, 3]

Complexity

Create sliceO(1)
Access by indexO(1)
SearchO(n)
CopyO(n)

When to use

  • +Parsing strings or binary data without copies
  • +Processing sub-arrays without allocation
  • +High-performance, zero-allocation code paths
  • +Interop with native or unmanaged memory
Go
// Slices ARE memory views in Go (like Span)
data := []int{1, 2, 3, 4, 5}

// Zero-copy slice - shares underlying array
slice := data[1:4]               // O(1) -> [2, 3, 4]
slice[0] = 20                    // mutates data: [1, 20, 3, 4, 5]

// Cap reveals underlying capacity
fmt.Println(len(slice), cap(slice)) // 3, 4

// Full slice expression - limits capacity
safe := data[1:4:4]             // O(1) len=3, cap=3
// append on safe won't overwrite data[4]

// Copy to new backing array (breaks sharing)
clone := make([]int, len(slice))
copy(clone, slice)               // O(n)

// unsafe.Slice for raw memory views (advanced)
// ptr := unsafe.SliceData(data)
// view := unsafe.Slice(ptr, len(data))

Big O Comparison

Average-case time complexity. * = amortized.

StructureAccessSearchInsertDelete
ArrayO(1)O(n)O(n)O(n)
Dynamic ArrayO(1)O(n)O(1)*O(n)
StackO(n)O(n)O(1)*O(1)
QueueO(n)O(n)O(1)*O(1)
Hash MapO(1)O(1)O(1)*O(1)
Hash SetN/AO(1)O(1)*O(1)
Linked ListO(n)O(n)O(1)O(1)
Sorted SetO(n)O(log n)O(log n)O(log n)
Sorted MapO(log n)O(log n)O(log n)O(log n)
Priority QueueO(n)O(n)O(log n)O(log n)
Concurrent MapO(1)O(1)O(1)*O(1)
Memory ViewO(1)O(n)N/AN/A

Which collection should I use?

I need to...Use
Store items by index, resize dynamicallyList / Dynamic Array
Map keys to values with O(1) lookupHashMap / Dictionary
Track unique items, check existence in O(1)HashSet / Set
Last-in-first-out (undo, DFS, brackets)Stack
First-in-first-out (BFS, task queues)Queue
Keep elements sorted at all timesSortedSet / TreeSet
Process items by priority (Dijkstra, top-K)PriorityQueue / Heap
Insert/delete at a known position in O(1)LinkedList
Sorted key-value pairsSortedDictionary / TreeMap
Thread-safe shared cacheConcurrentDictionary
Slice arrays/strings without copyingSpan / Slice / memoryview

Frequently Asked Questions

What are the most important data structures in Go?add

The most commonly used are dynamic arrays (List/ArrayList/vector), hash maps (Dictionary/HashMap/dict), and hash sets. For interviews, also know stacks, queues, trees, and priority queues. These cover 90%+ of coding interview problems.

Which Go data structure should I learn first?add

Start with the dynamic array and hash map. Together they solve the majority of interview problems. Then learn stacks (for DFS, bracket matching) and queues (for BFS). After that, tackle trees, heaps, and graphs.

Does Big O complexity change between languages?add

No. Big O measures algorithmic complexity, not language-specific performance. A hash map lookup is O(1) whether you use Python dict, Java HashMap, or C# Dictionary. Constant factors differ (C++ is faster than Python in wall-clock time), but Big O is the same.

Is there a built-in priority queue in Go?add

Yes, via container/heap. You implement the heap.Interface (Len, Less, Swap, Push, Pop) on your own type.

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