docs: dsa.md

Fraguinha · Nov 24, 2024 · f56c670 · f56c670
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+---
+title: "DSA - Data Structures"
+description: "Data Structures in Java"
+date: 2024-09-26T12:00:00+01:00
+draft: false
+---
+
+Overview of the most useful data structures from the Java Collections API
+
+# Arrays
+
+**Array**
+
+{{< highlight java >}}
+E[] array = new E[10];
+int n = array.length;
+
+E element = array[0];
+array[0] = element;
+
+Arrays.sort(array);
+Arrays.sort(array, Collections.reverseOrder());
+Arrays.sort(array, (E e1, E e2) -> e1.compareTo(e2));
+
+int index = Arrays.binarySearch(array, element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Access    | O(1)            |
+| Update    | O(1)            |
+| Iteration | O(n)            |
+
+---
+
+# Dynamic Array
+
+**ArrayList**
+
+{{< highlight java >}}
+ArrayList<E> list = new ArrayList<>();
+int n = list.size();
+
+list.add(element);
+list.add(index, element);
+list.addAll(collection);
+list.addAll(index, collection);
+
+E element = list.get(index);
+
+E removed = list.remove(index);
+list.clear();
+
+boolean isEmpty = list.isEmpty();
+boolean contains = list.contains(element);
+int index = list.indexOf(element);
+
+Collections.sort(list);
+Collections.sort(list, Collections.reverseOrder());
+Collections.sort(list, (E e1, E e2) -> e1.compareTo(e2));
+
+int index = Collections.binarySearch(list, element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Get       | O(1)            |
+| IndexOf   | O(n)            |
+| Add       | O(1)            |
+| Remove    | O(n)            |
+| Iteration | O(n)            |
+
+---
+
+# Lists
+
+**LinkedList**
+
+{{< highlight java >}}
+LinkedList<E> list = new LinkedList<>();
+int n = list.size();
+
+list.add(element);
+list.add(index, element);
+list.addAll(collection);
+list.addAll(index, collection);
+
+E element = list.get(index);
+
+E removed = list.remove(index);
+list.clear();
+
+boolean isEmpty = list.isEmpty();
+boolean contains = list.contains(element);
+int index = list.indexOf(element);
+
+Collections.sort(list);
+Collections.sort(list, Collections.reverseOrder());
+Collections.sort(list, (E e1, E e2) -> e1.compareTo(e2));
+
+int index = Collections.binarySearch(list, element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Get       | O(n)            |
+| IndexOf   | O(n)            |
+| Add       | O(n)            |
+| Remove    | O(n)            |
+| Iteration | O(n)            |
+
+---
+
+# Stacks
+
+**ArrayDeque**
+
+{{< highlight java >}}
+ArrayDeque<E> stack = new ArrayDeque<>();
+
+stack.push(element);
+E top = stack.peek();
+E popped = stack.pop();
+
+boolean isEmpty = stack.isEmpty();
+int size = stack.size();
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Push      | O(1)            |
+| Peek      | O(1)            |
+| Pop       | O(1)            |
+
+---
+
+# Queues
+
+**ArrayDeque**
+
+{{< highlight java >}}
+ArrayDeque<E> queue = new ArrayDeque<>();
+
+queue.offer(element);
+E head = queue.peek();
+E removed = queue.poll();
+
+boolean isEmpty = queue.isEmpty();
+int size = queue.size();
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Offer     | O(1)            |
+| Peek      | O(1)            |
+| Poll      | O(1)            |
+
+**PriorityQueue** (Heap Implementation)
+
+{{< highlight java >}}
+PriorityQueue<E> priorityQueue = new PriorityQueue<>();
+PriorityQueue<E> priorityQueue = new PriorityQueue<>(Collections.reverseOrder());
+PriorityQueue<E> priorityQueue = new PriorityQueue<>((E e1, E e2) -> e1.compareTo(e2));
+int size = priorityQueue.size();
+
+priorityQueue.offer(element);
+E head = priorityQueue.peek();
+E removed = priorityQueue.poll();
+
+boolean isEmpty = priorityQueue.isEmpty();
+boolean contains = priorityQueue.contains(element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Offer     | O(log n)        |
+| Peek      | O(1)            |
+| Poll      | O(log n)        |
+
+---
+
+# Sets
+
+**HashSet**
+
+{{< highlight java >}}
+HashSet<E> set = new HashSet<>();
+int n = set.size();
+
+set.add(element);
+
+set.remove(element);
+set.clear();
+
+boolean isEmpty = set.isEmpty();
+boolean contains = set.contains(element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity                              |
+| --------- | -------------------------------------------- |
+| Add       | O(1) (degrades to O(n) with hash collisions) |
+| Remove    | O(1) (degrades to O(n) with hash collisions) |
+| Contains  | O(1) (degrades to O(n) with hash collisions) |
+| Iteration | O(n)                                         |
+
+**TreeSet**
+
+{{< highlight java >}}
+TreeSet<E> set = new TreeSet<>();
+TreeSet<E> set = new TreeSet<>(Collections.reverseOrder());
+TreeSet<E> set = new TreeSet<>((E e1, E e2) -> e1.compareTo(e2));
+int n = set.size();
+
+set.add(element);
+
+E first = set.first();
+E last = set.last();
+
+E before = set.lower(element);
+E after = set.higher(element);
+
+set.remove(element);
+set.clear();
+
+SortedSet<E> sub = set.subSet(fromElement, fromInclusive, toElement, toInclusive);
+SortedSet<E> tail = set.tailSet(fromElement, inclusive);
+SortedSet<E> head = set.headSet(toElement, inclusive);
+
+boolean isEmpty = set.isEmpty();
+boolean contains = set.contains(element);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity |
+| --------- | --------------- |
+| Add       | O(log n)        |
+| Remove    | O(log n)        |
+| Contains  | O(log n)        |
+| Iteration | O(n)            |
+
+**LinkedHashSet**
+
+{{< highlight java >}}
+LinkedHashSet<E> set = new LinkedHashSet<>();
+int n = set.size();
+
+set.add(element);
+set.remove(element);
+set.clear();
+
+boolean isEmpty = set.isEmpty();
+boolean contains = set.contains(element);
+
+Iterator<E> iterator = set.iterator();
+
+// insertion order iteration
+for (E e : set) {
+
+}
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation | Time Complexity                              |
+| --------- | -------------------------------------------- |
+| Add       | O(1) (degrades to O(n) with hash collisions) |
+| Remove    | O(1) (degrades to O(n) with hash collisions) |
+| Contains  | O(1) (degrades to O(n) with hash collisions) |
+| Iteration | O(n)                                         |
+
+---
+
+# Maps
+
+**HashMap**
+
+{{< highlight java >}}
+HashMap<K, V> map = new HashMap<>();
+int n = map.size();
+
+map.put(key, value);
+
+V value = map.get(key);
+
+map.remove(key);
+map.clear();
+
+boolean isEmpty = map.isEmpty();
+boolean containsKey = map.containsKey(key);
+boolean containsValue = map.containsValue(value);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation     | Time Complexity                              |
+| ------------- | -------------------------------------------- |
+| Put           | O(1) (degrades to O(n) with hash collisions) |
+| Get           | O(1) (degrades to O(n) with hash collisions) |
+| Remove        | O(1) (degrades to O(n) with hash collisions) |
+| ContainsKey   | O(1) (degrades to O(n) with hash collisions) |
+| ContainsValue | O(n)                                         |
+| Iteration     | O(n)                                         |
+
+**TreeMap**
+
+{{< highlight java >}}
+TreeMap<K, V> map = new TreeMap<>();
+TreeMap<K, V> map = new TreeMap<>(Collections.reverseOrder());
+TreeMap<K, V> map = new TreeMap<>((K k1, K k2) -> k1.compareTo(k2));
+int n = map.size();
+
+map.put(key, value);
+
+V value = map.get(key);
+
+K firstKey = map.firstKey();
+K lastKey = map.lastKey();
+
+K beforeKey = map.lowerKey(key);
+K afterKey = map.higherKey(key);
+
+map.remove(key);
+map.clear();
+
+NavigableMap<K, V> sub = map.subMap(fromKey, fromInclusive, toKey, toInclusive);
+NavigableMap<K, V> tail = map.tailMap(fromKey, inclusive);
+NavigableMap<K, V> head = map.headMap(toKey, inclusive);
+
+boolean isEmpty = map.isEmpty();
+boolean containsKey = map.containsKey(key);
+boolean containsValue = map.containsValue(value);
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation     | Time Complexity |
+| ------------- | --------------- |
+| Put           | O(log n)        |
+| Get           | O(log n)        |
+| Remove        | O(log n)        |
+| ContainsKey   | O(log n)        |
+| ContainsValue | O(n)            |
+| Iteration     | O(n)            |
+
+**LinkedHashMap**
+
+{{< highlight java >}}
+LinkedHashMap<E> map = new LinkedHashMap<>();
+LinkedHashMap<E> map = new LinkedHashMap<>(Collections.reverseOrder());
+LinkedHashMap<E> map = new LinkedHashMap<>((E e1, E e2) -> e1.compareTo(e2));
+int n = map.size();
+
+map.add(element);
+map.remove(element);
+map.clear();
+
+boolean isEmpty = map.isEmpty();
+boolean contains = map.contains(element);
+
+Iterator<E> iterator = map.iterator();
+
+// insertion order iteration
+for (Map.Entry<K, V> entry : map.entrySet()) {
+  K key = entry.getKey();
+  V value = entry.getValue();
+}
+{{< / highlight >}}
+
+**Running times**:
+
+| Operation     | Time Complexity                              |
+| ------------- | -------------------------------------------- |
+| Put           | O(1) (degrades to O(n) with hash collisions) |
+| Get           | O(1) (degrades to O(n) with hash collisions) |
+| Remove        | O(1) (degrades to O(n) with hash collisions) |
+| ContainsKey   | O(1) (degrades to O(n) with hash collisions) |
+| ContainsValue | O(n)                                         |
+| Iteration     | O(n)                                         |