Java算法常用技巧

一、排序

资料：https://blog.csdn.net/weixin_72499901/article/details/136592073

正排序

import java.util.Arrays;public class SortArray {public static void main(String[] args) {int[] citations = {5, 3, 8, 2, 1, 4};// 打印原数组System.out.println("原数组: " + Arrays.toString(citations));// 使用 Arrays.sort() 进行排序Arrays.sort(citations);// 打印排序后的数组System.out.println("排序后的数组: " + Arrays.toString(citations));}
}

降序排序

这个只能处理包装，处理Integer,不能处理int

public static void main(String[] args) {Integer[] citations = {5, 3, 8, 2, 1, 4};// 打印原数组System.out.println("原数组: " + Arrays.toString(citations));// 使用 Arrays.sort() 进行降序排序Arrays.sort(citations, Collections.reverseOrder());// 打印排序后的数组System.out.println("排序后的数组: " + Arrays.toString(citations));}

处理数组

Integer[] arr = {5,4,7,9,2,12,54,21,1};//降序Arrays.sort(arr, new Comparator<Integer>() {//重写compare方法，最好加注解，不加也没事public int compare(Integer a, Integer b) {//返回值>0交换return b-a;}});

二、初始化

自己对于列表，数组的初始化还是不太熟悉

1. 数组的初始化

int[] a = {1,2,3,4};

2. Java List的初始化

用数组初始化List

 Integer [] a = {1,2,34};List<Integer> list = Arrays.asList(a);list.stream().forEach(System.out::println);

直接初始化

 List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4));list.stream().forEach(System.out::println);

List<Integer> list = new ArrayList<>();
Collections.addAll(list, 1, 2, 3, 4, 5);

数组增加在指定位置

List<Integer> list= new LinkedList<>(Arrays.asList(1,3,4));list.add(2,5);list.stream().forEach(System.out::println);

3. 数组转为List

citations 是int数组

List<Integer> citationList = IntStream.of(citations).boxed().toList();

Java stream语法

 int[][] intervals = {{1, 3},{2, 4},{5, 7},{6, 8}};Arrays.stream(intervals).skip(2).limit(2).forEach(a -> System.out.println(a[0] +" "+ a[1]));

skip 就是跳过前两个，limit 表示只输出两个，所以输出的是

数据结构

1. queue

Queue<String> queue = new LinkedList<String>();
//添加元素
queue.offer("a");
queue.poll() // 删除并返回
queue.peek()//只返回

https://www.liaoxuefeng.com/wiki/1252599548343744/1265121791832960
https://www.runoob.com/java/data-queue.html

2. stack

压入元素 (push):
弹出元素 (pop):从栈顶移除并返回元素。
查看栈顶元素 (peek):查看栈顶元素但不移除它。
查找元素 (search):

import java.util.Stack;public class StackExample {public static void main(String[] args) {// 创建一个 StackStack<Integer> stack = new Stack<>();// 压入元素stack.push(10);stack.push(20);stack.push(30);System.out.println("Stack after pushing: " + stack);// 查看栈顶元素System.out.println("Top element is: " + stack.peek());// 弹出元素System.out.println("Popped element: " + stack.pop());System.out.println("Stack after popping: " + stack);// 查找元素int position = stack.search(10);if (position != -1) {System.out.println("Element 10 found at position: " + position);} else {System.out.println("Element 10 not found.");}// 检查是否为空System.out.println("Is stack empty? " + stack.isEmpty());}
}

stack 转化list
List list = stack.stream().toList();

stack 循环

 Iterator<Integer> iterator = stack.iterator();while (iterator.hasNext()) {System.out.print(iterator.next() + " ");}