Java

HashSet

contains  add

Stack

empty peek pop push(add) size

HashMap

map.keySet()
valueOf(value)
get(key), put(key, value), isEmpty()
map.getOrDefault(Object key, V defaultValue)
containsKey(key) containsValue(value) remove(key)
cnt.merge(x, 1, Integer::sum);

Queue

Queue<TreeNode> q = new LinkedList<>();
offer(*) poll() peek() isEmpty()

PriorityQueue<int> heap = new PriorityQueue<int>(); //小顶堆
PriorityQueue<int> heap = new PriorityQueue<>((a, b) -> b - a); //大顶堆
PriorityQueue<Double> q = new PriorityQueue<>((a, b) -> b.compareTo(a));
PriorityQueue<Integer> q = new PriorityQueue<Integer>(new Comparator<Integer>() {
    @Override
    public int compare(Integer o1, Integer o2) {
        return o1 - o2;
    }
});

Deque

Deque<Integer> q = new ArrayDeque<>(); //双端队列 ，栈
Deque<Integer> stack = new LinkedList<>();
isEmpty() peek() poll()

String

s.charAt(i)
s.toCharArray()；
String.valueOf

Arrays

Arrays.fill
Arrays.sort

Integer

Integer.toBinaryString(i);