Java中一些常见排序算法
冒泡排序（Bubble Sort）：public class BubbleSort {
public static void bubbleSort(int[] arr) {
int n = arr.length;
for (int i = 0; i < n-1; i++) {
for (int j = 0; j < n-i-1; j++) {
if (arr > arr) {
// 交换arr和arr
int temp = arr;
arr = arr;
arr = temp;
}
}
}
}
}
选择排序（Selection Sort）：
public class SelectionSort {
public static void selectionSort(int[] arr) {
int n = arr.length;
for (int i = 0; i < n-1; i++) {
int minIndex = i;
for (int j = i+1; j < n; j++) {
if (arr < arr) {
minIndex = j;
}
}
// 交换arr和arr
int temp = arr;
arr = arr;
arr = temp;
}
}
}
插入排序（Insertion Sort）：
public class InsertionSort {
public static void insertionSort(int[] arr) {
int n = arr.length;
for (int i = 1; i < n; ++i) {
int key = arr;
int j = i - 1;
while (j >= 0 && arr > key) {
arr = arr;
j = j - 1;
}
arr = key;
}
}
}
public class ShellSort {
public static void shellSort(int[] arr) {
int n = arr.length;
for (int gap = n / 2; gap > 0; gap /= 2) {
for (int i = gap; i < n; i++) {
int temp = arr;
int j = i;
while (j >= gap && arr > temp) {
arr = arr;
j -= gap;
}
arr = temp;
}
}
}
}
public class MergeSort {
public static void mergeSort(int[] arr, int l, int r) {
if (l < r) {
int m = l + (r - l) / 2;
mergeSort(arr, l, m);
mergeSort(arr, m + 1, r);
merge(arr, l, m, r);
}
}
private static void merge(int[] arr, int l, int m, int r) {
int n1 = m - l + 1;
int n2 = r - m;
int[] L = new int;
int[] R = new int;
System.arraycopy(arr, l, L, 0, n1);
System.arraycopy(arr, m + 1, R, 0, n2);
int i = 0, j = 0, k = l;
while (i < n1 && j < n2) {
if (L <= R) {
arr = L;
} else {
arr = R;
}
}
while (i < n1) {
arr = L;
}
while (j < n2) {
arr = R;
}
}
}
public class QuickSort {
public static void quickSort(int[] arr, int low, int high) {
if (low < high) {
int pi = partition(arr, low, high);
quickSort(arr, low, pi - 1);
quickSort(arr, pi + 1, high);
}
}
private static int partition(int[] arr, int low, int high) {
int pivot = arr;
int i = low - 1;
for (int j = low; j < high; j++) {
if (arr < pivot) {
i++;
int temp = arr;
arr = arr;
arr = temp;
}
}
int temp = arr;
arr = arr;
arr = temp;
return i + 1;
}
}
public class HeapSort {
public static void heapSort(int[] arr) {
int n = arr.length;
for (int i = n / 2 - 1; i >= 0; i--) {
heapify(arr, n, i);
}
for (int i = n - 1; i > 0; i--) {
int temp = arr;
arr = arr;
arr = temp;
heapify(arr, i, 0);
}
}
private static void heapify(int[] arr, int n, int i) {
int largest = i;
int left = 2 * i + 1;
int right = 2 * i + 2;
if (left < n && arr > arr) {
largest = left;
}
if (right < n && arr > arr) {
largest = right;
}
if (largest != i) {
int temp = arr;
arr = arr;
arr = temp;
heapify(arr, n, largest);
}
}
}
来个跳表算法，根本不用排序，插入/删除就决定了元素的位置，redis内核有用这个算法
import java.util.Random;
class Node {
int value;
Node[] nextNodes = new Node; // 假设最大层级为16
Node(int value) {
this.value = value;
}
}
public class SkipList {
private final Random random = new Random();
private Node head;
private int levelCount = 1; // 当前跳表层级数
public SkipList() {
head = new Node(Integer.MIN_VALUE);
for (int i = 0; i < nextNodes.length; i++) {
head.nextNodes = null;
}
}
// 插入节点
public void insert(int value) {
Node newNode = new Node(value);
Node current = head;
int newLevel = randomLevel(); // 随机生成新节点的层级
if (newLevel > levelCount) {
levelCount = newLevel;
}
// 从最高层开始插入
for (int i = levelCount - 1; i >= 0; i--) {
while (current.nextNodes != null && current.nextNodes.value < value) {
current = current.nextNodes;
}
newNode.nextNodes = current.nextNodes;
current.nextNodes = newNode;
}
}
// 查找节点
public boolean contains(int value) {
Node current = head;
for (int i = levelCount - 1; i >= 0; i--) {
while (current.nextNodes != null && current.nextNodes.value < value) {
current = current.nextNodes;
}
if (current.nextNodes != null && current.nextNodes.value == value) {
return true;
}
}
return false;
}
// 删除节点
public void delete(int value) {
Node[] update = new Node; // 更新路径数组
Node current = head;
for (int i = levelCount - 1; i >= 0; i--) {
while (current.nextNodes != null && current.nextNodes.value < value) {
current = current.nextNodes;
}
update = current;
}
if (current.nextNodes != null && current.nextNodes.value == value) {
current = current.nextNodes;
for (int i = levelCount - 1; i >= 0; i--) {
if (update.nextNodes == current) {
update.nextNodes = current.nextNodes;
}
}
// 如果层级计数过高，则向下调整
while (levelCount > 1 && head.nextNodes == null) {
levelCount--;
}
}
}
// 随机生成节点的层级
private int randomLevel() {
int lvl = 1;
while (random.nextDouble() < 0.5 && lvl < nextNodes.length) {
lvl++;
}
return lvl;
}
} 学习了，学习了！ 学到了，总结提炼成子程序，真是科研狗的干活利器啊！ zyc1996 发表于 2024-3-14 19:44
您好，我想问一下，我是做大数据的，主要是数仓开发，对后端java不太懂，如果想学的话，怎么开始比较好呢
先从java基础学习 可以参考如下方向
基础知识学习： 从Java的基础知识开始学起，掌握Java的语法、面向对象编程等基本概念。
学习Java后端开发框架： 了解常用的Java后端开发框架，比如Spring Framework，Spring Boot等。这些框架能够帮助你快速搭建Java后端应用程序。
实践项目： 通过实践项目来巩固所学知识。你可以选择一些小型的项目来开始，逐渐增加复杂度，比如简单的Web应用或者RESTful API。
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