public class Node{ int value; Node next; public static void main(String args[]){ Node h =new Node(); Node p=h; for (int k=1;k<=4;k++) { p.value = 10 - k; Node q = new Node(); p.next = q; p = q; } p=h; while (p!=null){ System.out.println(p.value); p=p.next; } } }
时间: 2024-02-14 19:09:41 浏览: 34
这段Java代码创建了一个链表,链表中每个节点都包含一个整数值和一个指向下一个节点的引用。链表中共有4个节点。
在代码中,首先创建了一个头节点h,然后创建一个指针p指向头节点。接着用for循环创建了4个新节点,并将它们依次连接到链表中。循环结束后,将指针p重新指向头节点h。
最后,通过while循环,遍历整个链表,输出每个节点的值。
输出结果为:
9
8
7
6
相关问题
import java.io.BufferedReader; import java.io.File; import java.io.FileReader; import java.io.IOException; public class TSPSolver { public static void main(String[] args) throws IOException { String filePath = "mu1979.tsp";//该文件放在Java的包中 TSPSolver solver=new TSPSolver(); solver.readTSP(filePath); } public void readTSP(String fileName) throws IOException { File file = new File(fileName); BufferedReader br = new BufferedReader(new FileReader(file)); String line; int numNodes = 0; double[][] nodes = null; while ((line = br.readLine()) != null) { if (line.startsWith("DIMENSION")) { // 获取节点数量 String[] parts = line.split(":"); numNodes = Integer.parseInt(parts[1].trim()); nodes = new double[numNodes][2]; } else if (line.startsWith("NODE_COORD_SECTION")) { // 读取节点坐标 for (int i = 0; i < numNodes; i++) { line = br.readLine(); String[] parts = line.split("\s+"); nodes[i][0] = Double.parseDouble(parts[1]); nodes[i][1] = Double.parseDouble(parts[2]); } } } br.close(); // 计算节点之间的距离 double[][] distance = new double[numNodes][numNodes]; for (int i = 0; i < numNodes; i++) { for (int j = 0; j < numNodes; j++) { double dx = nodes[i][0] - nodes[j][0]; double dy = nodes[i][1] - nodes[j][1]; distance[i][j] = Math.sqrt(dxdx + dydy); } } // 贪心算法求解TSP问题 int start = 0; boolean[] visited = new boolean[numNodes]; visited[start] = true; int[] path = new int[numNodes]; path[0] = start; for (int i = 1; i < numNodes; i++) { int next = -1; double minDist = Double.MAX_VALUE; for (int j = 0; j < numNodes; j++) { if (!visited[j] && distance[start][j] < minDist) { next = j; minDist = distance[start][j]; } } visited[next] = true; path[i] = next; start = next; } // 输出结果 System.out.print("Path: "); for (int i = 0; i < numNodes; i++) { System.out.print(path[i] + "->"); if((i+1)%20==0) System.out.println(); } } }这段代码是用贪心法求解商旅问题,请将其改成用动态规划方法解决商旅问题
商旅问题是一个NP完全问题,使用动态规划算法求解比较困难。一种可行的方法是使用分支限界算法或遗传算法等启发式方法。以下是一个使用遗传算法求解商旅问题的Java代码,供您参考:
```java
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Arrays;
import java.util.Random;
public class TSPSolver_DP {
static class City {
double x;
double y;
public City(double x, double y) {
this.x = x;
this.y = y;
}
public double distanceTo(City other) {
double dx = x - other.x;
double dy = y - other.y;
return Math.sqrt(dx * dx + dy * dy);
}
}
static class Individual implements Comparable<Individual> {
int[] path;
double fitness;
public Individual(int[] path, double fitness) {
this.path = path;
this.fitness = fitness;
}
@Override
public int compareTo(Individual o) {
return Double.compare(fitness, o.fitness);
}
}
private int numCities;
private City[] cities;
private Random random = new Random();
public static void main(String[] args) throws IOException {
String filePath = "mu1979.tsp";
TSPSolver_DP solver = new TSPSolver_DP();
solver.readTSP(filePath);
solver.solveTSP(100, 10000, 0.8, 0.1);
}
public void readTSP(String fileName) throws IOException {
File file = new File(fileName);
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
if (line.startsWith("DIMENSION")) {
numCities = Integer.parseInt(line.split(":")[1].trim());
cities = new City[numCities];
} else if (line.startsWith("NODE_COORD_SECTION")) {
for (int i = 0; i < numCities; i++) {
line = br.readLine();
String[] parts = line.split("\\s+");
cities[i] = new City(Double.parseDouble(parts[1]), Double.parseDouble(parts[2]));
}
}
}
br.close();
}
public void solveTSP(int populationSize, int numGenerations, double crossoverRate, double mutationRate) {
Individual[] population = initializePopulation(populationSize);
for (int i = 0; i < numGenerations; i++) {
Arrays.sort(population);
System.out.printf("Generation %d: Best fitness = %f\n", i, population[0].fitness);
population = evolvePopulation(population, crossoverRate, mutationRate);
}
System.out.printf("Best path: ");
for (int i = 0; i < numCities; i++) {
System.out.printf("%d->", population[0].path[i]);
if ((i + 1) % 20 == 0) {
System.out.println();
}
}
System.out.printf("%d\n", population[0].path[0]);
}
private Individual[] initializePopulation(int populationSize) {
Individual[] population = new Individual[populationSize];
for (int i = 0; i < populationSize; i++) {
int[] path = new int[numCities];
for (int j = 0; j < numCities; j++) {
path[j] = j;
}
shuffle(path);
double fitness = evaluateFitness(path);
population[i] = new Individual(path, fitness);
}
return population;
}
private void shuffle(int[] array) {
for (int i = 0; i < array.length; i++) {
int j = random.nextInt(array.length - i) + i;
swap(array, i, j);
}
}
private void swap(int[] array, int i, int j) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
private double evaluateFitness(int[] path) {
double distance = 0;
for (int i = 0; i < numCities; i++) {
distance += cities[path[i]].distanceTo(cities[path[(i + 1) % numCities]]);
}
return 1 / distance;
}
private Individual[] evolvePopulation(Individual[] population, double crossoverRate, double mutationRate) {
Individual[] nextGeneration = new Individual[population.length];
for (int i = 0; i < population.length; i++) {
Individual parent1 = selectParent(population);
Individual parent2 = selectParent(population);
Individual offspring = crossover(parent1, parent2, crossoverRate);
mutate(offspring, mutationRate);
double fitness = evaluateFitness(offspring.path);
nextGeneration[i] = new Individual(offspring.path, fitness);
}
return nextGeneration;
}
private Individual selectParent(Individual[] population) {
int index = random.nextInt(population.length);
return population[index];
}
private Individual crossover(Individual parent1, Individual parent2, double crossoverRate) {
if (random.nextDouble() < crossoverRate) {
int index1 = random.nextInt(numCities);
int index2 = random.nextInt(numCities);
if (index1 > index2) {
int temp = index1;
index1 = index2;
index2 = temp;
}
int[] offspringPath = new int[numCities];
Arrays.fill(offspringPath, -1);
for (int i = index1; i <= index2; i++) {
offspringPath[i] = parent1.path[i];
}
int j = 0;
for (int i = 0; i < numCities; i++) {
if (j == index1) {
j = index2 + 1;
}
if (contains(offspringPath, parent2.path[i])) {
continue;
}
while (offspringPath[j] != -1) {
j = (j + 1) % numCities;
}
offspringPath[j] = parent2.path[i];
j = (j + 1) % numCities;
}
return new Individual(offspringPath, evaluateFitness(offspringPath));
} else {
return parent1;
}
}
private boolean contains(int[] array, int value) {
for (int i = 0; i < array.length; i++) {
if (array[i] == value) {
return true;
}
}
return false;
}
private void mutate(Individual individual, double mutationRate) {
for (int i = 0; i < numCities; i++) {
if (random.nextDouble() < mutationRate) {
int j = random.nextInt(numCities);
swap(individual.path, i, j);
}
}
}
}
```
该程序假设文件“mu1979.tsp”包含以下格式的数据:
```
DIMENSION: 1979
NODE_COORD_SECTION
1 0.00000 0.00000
2 0.00000 1.00000
...
```
程序读取数据并使用遗传算法求解商旅问题,输出结果包括最优路径和最优路径长度。
jsonnode转成jsonmap
要将 `JsonNode` 转换为 `JsonMap`,你可以使用 Jackson 库提供的 API。下面是一个示例代码:
```java
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class JsonUtils {
public static JsonMap convertToJsonMap(JsonNode jsonNode) {
JsonMap jsonMap = new JsonMap();
if (jsonNode.isObject()) {
Iterator<Entry<String, JsonNode>> fields = jsonNode.fields();
while (fields.hasNext()) {
Entry<String, JsonNode> field = fields.next();
jsonMap.put(field.getKey(), convertToJsonMap(field.getValue()));
}
} else if (jsonNode.isArray()) {
int index = 0;
for (JsonNode element : jsonNode) {
jsonMap.put(String.valueOf(index++), convertToJsonMap(element));
}
} else if (jsonNode.isValueNode()) {
jsonMap.put("value", jsonNode.asText());
}
return jsonMap;
}
public static void main(String[] args) throws Exception {
String jsonString = "{\"name\": \"John\", \"age\": 30, \"city\": \"New York\"}";
ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readTree(jsonString);
JsonMap jsonMap = convertToJsonMap(jsonNode);
System.out.println(jsonMap);
}
}
class JsonMap extends HashMap<String, Object> {
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("{");
for (Entry<String, Object> entry : entrySet()) {
sb.append("\"").append(entry.getKey()).append("\""); sb.append(": ");
Object value = entry.getValue();
if (value instanceof JsonMap) {
sb.append(value.toString());
} else {
sb.append("\"").append(value).append("\"");
}
sb.append(", ");
}
if (!isEmpty()) {
sb.setLength(sb.length() - 2);
}
sb.append("}");
return sb.toString();
}
}
```
以上代码将 `JsonNode` 对象转换为自定义的 `JsonMap` 对象,`JsonMap` 继承自 `HashMap<String, Object>`。你可以根据需要自定义 `JsonMap` 类的方法和字段。
在示例中,我们先将 `JsonNode` 对象转换为 `JsonMap` 对象,然后通过重写 `toString()` 方法将 `JsonMap` 转换为 JSON 字符串进行输出。
注意:为了运行示例代码,你需要将 Jackson 库添加到项目依赖中。你可以在 Maven 或 Gradle 中添加以下依赖:
Maven:
```xml
<dependencies>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.12.5</version>
</dependency>
</dependencies>
```
Gradle:
```groovy
dependencies {
implementation 'com.fasterxml.jackson.core:jackson-databind:2.12.5'
}
```
希望能对你有所帮助!如有其他问题,请随时提问。
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