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线性搜索(Linear Search),也称为顺序搜索,是最基本的搜索算法之一。它的工作原理是通过遍历数组或列表中的每一个元素,直到找到目标值为止,或者遍历完所有元素后确定目标值不存在于列表中。
线性搜索的时间复杂度为O(n),其中n是列表中元素的数量。这是因为最坏情况下,你可能需要检查列表中的每一个元素才能找到目标值或确定它不在列表中。
下面是一个简单的Java代码示例,演示如何实现线性搜索:
public class LinearSearch { /** * Performs linear search on an array to find a target value. * * @param array The array of integers to search through. * @param target The integer value to search for. * @return The index of the target if found, otherwise -1. */ public static int linearSearch(int[] array, int target) { for (int i = 0; i < array.length; i++) { if (array[i] == target) { return i; // Target found, return its index. } } return -1; // Target not found. } public static void main(String[] args) { int[] data = {5, 3, 9, 2, 8}; int target = 9; int index = linearSearch(data, target); if (index != -1) { System.out.println("Element " + target + " found at index " + index); } else { System.out.println("Element " + target + " not found"); } } }
初始化:定义一个变量i
作为索引,从0开始。
遍历数组:使用for循环遍历数组中的每一个元素,直到到达数组的末尾。
比较元素:在每一次循环中,将当前元素array[i]
与目标值target
进行比较。
找到目标值:如果array[i]
等于target
,则返回当前的索引i
,表示目标值在数组中的位置。
未找到目标值:如果循环结束时仍未找到目标值,则返回-1,表示目标值不在数组中。
输出结果:根据返回的索引值判断目标值是否找到,并输出相应的信息。
通过这个示例和解析,你可以更好地理解线性搜索算法的工作原理以及如何在Java中实现它。
如果你想要扩展线性搜索的代码,可以考虑添加一些额外的功能,比如处理可能的异常、增强输出信息、允许用户输入数据等。下面是一个扩展后的Java程序,它包含了这些功能:
import java.util.Scanner; public class ExtendedLinearSearch { /** * Performs linear search on an array to find a target value. * * @param array The array of integers to search through. * @param target The integer value to search for. * @return The index of the target if found, otherwise -1. */ public static int linearSearch(int[] array, int target) { for (int i = 0; i < array.length; i++) { if (array[i] == target) { return i; // Target found, return its index. } } return -1; // Target not found. } public static void main(String[] args) { Scanner scanner = new Scanner(System.in); // Ask user to enter the size of the array System.out.print("Enter the number of elements in the array: "); int size = scanner.nextInt(); // Create an array of given size and ask user to fill it int[] data = new int[size]; System.out.println("Enter the elements of the array:"); for (int i = 0; i < size; i++) { data[i] = scanner.nextInt(); } // Ask user to enter the target value System.out.print("Enter the target value to search: "); int target = scanner.nextInt(); // Perform the search int index = linearSearch(data, target); // Check if the target was found and print the result if (index != -1) { System.out.println("Element " + target + " found at index " + index); } else { System.out.println("Element " + target + " not found"); } scanner.close(); } }
在这个扩展版本中,程序会:
此外,程序使用Scanner
类从用户那里获取输入,确保了与用户的交互性。这使得程序更加灵活,可以在不同的输入下运行。当程序结束时,记得关闭Scanner
对象以释放资源。
这样的代码扩展使得线性搜索算法更加实用和通用,可以应用于各种需要用户输入和动态数据处理的场景。
我们可以增加一些额外的功能,例如:
下面是包含上述功能的Java代码:
import java.util.Scanner; public class AdvancedLinearSearch { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); long totalSearchTime = 0L; int totalSearches = 0; // Ask user to enter the size of the array System.out.print("Enter the number of elements in the array: "); int size = getValidInteger(scanner); int[] data = new int[size]; // Create an array of given size and ask user to fill it System.out.println("Enter the elements of the array:"); for (int i = 0; i < size; i++) { data[i] = getValidInteger(scanner); } boolean continueSearching = true; while (continueSearching) { // Ask user to enter the target value System.out.print("Enter the target value to search (or 'q' to quit): "); String input = scanner.next(); if ("q".equals(input.toLowerCase())) { break; } int target = Integer.parseInt(input); // Record start time before search long startTime = System.currentTimeMillis(); // Perform the search int index = linearSearch(data, target); // Record end time after search long endTime = System.currentTimeMillis(); long elapsedTime = endTime - startTime; totalSearchTime += elapsedTime; totalSearches++; // Check if the target was found and print the result if (index != -1) { System.out.println("Element " + target + " found at index " + index); } else { System.out.println("Element " + target + " not found"); } System.out.println("Time taken for search: " + elapsedTime + " ms\n"); } // Print average search time if any searches were performed if (totalSearches > 0) { double averageSearchTime = (double) totalSearchTime / totalSearches; System.out.println("Average search time over " + totalSearches + " searches: " + averageSearchTime + " ms"); } scanner.close(); } private static int linearSearch(int[] array, int target) { for (int i = 0; i < array.length; i++) { if (array[i] == target) { return i; // Target found, return its index. } } return -1; // Target not found. } private static int getValidInteger(Scanner scanner) { while (!scanner.hasNextInt()) { System.out.print("Invalid input! Please enter a valid integer: "); scanner.next(); // discard invalid token } return scanner.nextInt(); } }
在这个版本中,我们增加了以下功能:
getValidInteger()
方法用于确保从用户那里获取的输入是一个有效的整数,如果不是,会提示用户重新输入。这些额外的功能使得程序更加健壮和用户友好,同时也便于性能分析。
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