TreeMap/TreeSet
//[From](https://leetcode.com/problems/falling-squares/discuss/112678/Treemap-solution-and-Segment-tree-(Java)-solution-with-lazy-propagation-and-coordinates-compression)
Integer from = treeMap.floorKey(start);
int height = treeMap.subMap(from, end).values().stream().max(Integer::compare).get();
// remove interval within [start, end)
int lastHeight = treeMap.floorEntry(end).getValue();
treeMap.put(start, height);
treeMap.put(end, lastHeight);
treeMap.keySet().removeAll(new HashSet<>(treeMap.subMap(start, false, end, false).keySet()));
//<=, >=
treeset.floor()/ceilling()
// <, >
treeset.lower()/higher()
treemap.floorEntry()/floorKey(), ceillingEntry()/ceillingKey()
// <, >
treemap.lowerEntry()/lowerKey(), higherEntry()/higherKey()ArrayDeque
- As stack or queue:
- its default iterator or stream is a queue: fifo
- Use iterator, for loop to access it, but not support random access like get(i)
Stream
// convert map to map
map.forEach((s, integer) -> map2.put(s, integer));
map.forEach(map2::put);
Map<String, Integer> map2 =
map.entrySet().stream().collect(Collectors.toMap(
e -> e.getKey(),e -> Integer.parseInt(e.getValue())
));
// Array to set
Arrays.stream(wrapperArray).collect(Collectors.toSet())
Arrays.stream(primitiveArray).boxed().collect(Collectors.toSet())
// to TreeSet
strStream.collect(Collectors.toCollection(TreeSet::new))
// Collectors
.collect(Collectors.joining( "," ))
count.put(word, count.getOrDefault(word, 0) + 1);
// computeIfAbsent returns latest value, prefer this over putIfAbsent
map.computeIfAbsent(key, k -> new PriorityQueue()).add(value);
// iterate
Stream.iterate(wordsSize - 1, li -> li - 1).limit(wordsSize);
Stream.iterate(1, i -> i <= 3, i -> i + 1)
Map<String, Long> counted = list.stream()
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
Map<Character, Long> astring.chars().mapToObj(ch -> (char) ch)
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));/* char[] to Stream */
Stream<Character> stream = CharBuffer.wrap(list).chars().mapToObj(ch -> (char)ch);
IntStream intStream = Arrays.stream(new int[] {});
/* int[] to Stream<Integer> */
Stream<Integer> i = Arrays.stream(new int[] {}).boxed();
/* IntStream to int[]*/
int[] array = intStream.mapToInt(i->i).toArray();
Stream.of(int1, int2, ...).min(Integer::compare).get();Optional
Optional.of(new Outer())
.map(Outer::getNested)
.map(Nested::getInner)
.map(Inner::getFoo)
.ifPresent(System.out::println);// UnModifiable collection
List.of(1, 2)
List.copyOf(aList)
Set.of(1, 2)
Map.of("k1", "v1")
IntStream.range(1, 10)
IntStream.rangeClosed(1, 10)
IntStream.iterate(0, x -> x < 3, x -> x + 1)
IntStream
.max/min/average.getAsInt()
.sum
Stream<Integer>
.collect(Collectors.averagingInt(i -> i))
.averagingInt
.min(max)By(comparator)
.joining(delimiter,prefix,suffix)
.partitioningBy(predicate)
articles.collect(
Collectors.groupingBy(
Article::getTag,
Collectors.summingInt(Article::getWordCount)));
// Convert list of Character to String
listCharacter.stream().map(String::valueOf).collect(Collectors.joining()); Collection
Misc
String.join(delimiter, elements);
new StringBuilder(word).reverse().toString()
/* number to char array */
char[] array = String.valueOf(number).toCharArray();
/* char[] to number, work with prefix 0 like 01 */
Integer.parseInt(new String(charArray))
Arrays.fill(array, fromIndex, toIndex, val)
Comparator.naturalOrder()/reverseOrder()
Optional<Integer> max = list.stream().max(Comparator.naturalOrder());
Optional<Integer> max = list.stream().reduce(Integer::max);
/*remove multiple keys from Map*/
map.keySet().removeAll(set);
/* [][] to List<List<>> */
List<List<String>> r = Arrays.stream([][]).map(s -> Arrays.stream(s)
.collect(Collectors.toList())).collect(Collectors.toList())
// Get max from Map<Integer, Map<Integer, Integer>>
map.values().stream().flatMap(tmp ->tmp.values().stream())
.max(Comparator.naturalOrder()).get()
new random.ints(streamSize, randomNumberOrigin, randomNumberBound)
Collections.reverse(collection);
// array head, tail pointer
int j = s.length() - 1 - i;
javafx.util.pair pair = new new Pair<>(key, value);
Map.entry entry = Map.entry(key, value)
Character.isLetter/isWhitespace
// [deepToString() works for both single and multidimensional, but doesn’t work single dimensional array of primitives](https://www.geeksforgeeks.org/arrays-deeptostring-in-java-with-example/)
Arrays.deepToString(array)/toString(array)
String bits = Integer.toBinaryString(n);
Integer.bitCount(n)
ManagementFactory.getGarbageCollectorMXBeans()