data-structures.md

Strings

Commonly used functions

// convert string to chracters
char[] chracters = "string".toCharArray();

// convert character to string
char[] chracters = ...
String string = new String(characters);

// append string
stringBuilder.append("string-to-be-appended");

// prepend string
stringBuilder.insert(0, "string-to-be-prepended");

Arrays

Commonly used functions

// prints the array for debugging
int[] nums = ...
String string = Arrays.toString(nums);

// in-place sorting
// O(n log n)
int[] nums = ...
Arrays.sort(nums);

// populate arrays with specified value
int[] nums = ...
Arrays.fill(nums, 0);

// copy 1 array into another
System.arraycopy(int[] src, int srcStart, int[] dest, int destStart, int srclength);

// splice an array
int[] splice = Arrays.copyOfRange(int[] src, int startIndex, int endIndexExclusive)

Big O

Operation	Big O
lookup	O(1)
insert / delete	O(n)

Map / HashMap

Commonly used functions

int num = ...

boolean contains = map.containsKey(num);

value = map.getOrDefault(key, defaultValue);
map.keySet();
map.values();

Big O

Every operation is O(1).

Set / HashSet

Commonly used functions

Set<Integer> set = new HashSet<>();
int num =...

set.add(num);
boolean contains = set.contains(num);
set.remove(num);

Big O

Every operation is O(1).

PriorityQueue (Binary heap)

// smallest to largest (natural order)
// min-heap where smallest element is at the top of the binary tree
PriorityQueue<Integer> queue = new PriorityQueue<>();

// custom ordering
// e.g. max-heap where largest element is at the top of the binary tree
PriorityQueue<Integer> queue = new PriorityQueue<>((Integer c1, Integer c2) ->
    Integer.compare(c2, c1) // largest to smallest
    );

// enqueue
queue.add(num);

// dequeue
int num = queue.poll();

Big O

Operation	Big O
poll	O(1)
insert / delete	O(log n)