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java - 如果我输入一个未在数组中定义的值，为什么二进制搜索方法会给我一个错误？

问题描述

二进制搜索方法由变量值中的用户输入驱动。然后通过二进制搜索方法找到用户给出的值。虽然当我输入一个由数组定义的值时它可以正常工作，但是当我输入一个不是由数组定义的值时，我会得到一个错误。我想阻止这种情况，但我不知道从哪里开始尝试这个问题。

我收到的错误是

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
        at project.project.binarySearchAscending(project.java:99)
        at project.project.binarySearchAscending(project.java:107)
        at project.project.binarySearchAscending(project.java:107)
        at project.project.main(project.java:31)

这是我的项目的代码

package project;

import java.io.*;
import java.util.*;
import java.util.Scanner;

public class project {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in); 
        int Size;//size of the array
        int order; // ascending or descending order
        int value;//this is for the value that you are looking for
        System.out.println("Put in the amount of expenses you have");
        Size = sc.nextInt();//User input for the amount of expenses
        System.out.println("put in all your expenses");
        int userInput[] = new int[Size];// what the users expenses are
        for (int i = 0; i < userInput.length; i++)//This loop is for if the i value is smaller than user input then put in more values to complete the array
            userInput[i] = sc.nextInt();
        System.out.println("do you want it ascending or descending order. If you want it in ascending press 1 or if you want descending press 2");
        order = sc.nextInt();// select if they wanted it in ascending or descending order
        System.out.print("expenses not sorted : ");
        printExpenses(userInput);//this is the method that prints out all the expenses
        if (order == 1) {
            expensesAscending(userInput);// If order is equal to one then sort in ascending else if it is equal to 2 then order it descending
        } else if (order == 2) {
            expensedescending(userInput);

        }
        System.out.println("what value are you looking for");
        value = sc.nextInt();
        if (order == 1) {int ans = binarySearchAscending(userInput, 0, Size, value);//use the binary search ascending method
        System.out.println(ans);
        if(ans == -1)
            System.out.println("value not found");
          else
            System.out.println("your expense is found at "  + ans + " and the value of the array is " + userInput[ans]);
    }else if (order==2) {int ans = binarySearchDescending(userInput, 0, Size, value);//use the binary search descending method
    System.out.println(ans);
    if(ans == -1)
        System.out.println("value not found");
      else
        System.out.println("your expense is found at " + ans + "and the value of the array is " + userInput[ans]);

    }}


    public static void printExpenses(int[] arr) {
        // this is were it is printed
        for (int i = 0; i < arr.length; i++) {//loops when i = to 0 and i is less than the length of the array then you should add one to the i value so that it could print out the entire array
            System.out.println(arr[i] + "$");
        }
    }

    public static void expensedescending(int arr[]) {
        // This is were the selection sort starts
        int N = arr.length;
        for (int i = 0; i < N; i++) {
            int small = arr[i];
            int pos = i;
            for (int j = i + 1; j < N; j++) {
                if (arr[j] > small) {
                    small = arr[j];
                    pos = j;
                }
            }
            int temp = arr[pos];
            arr[pos] = arr[i];
            arr[i] = temp;
            System.out.println(": ");
            // Printing array after pass
            printExpenses(arr);
        }
    }

    public static void expensesAscending(int arr[]) {
        //insertion sort
        int N = arr.length;
        for (int i = 1; i < N; i++) {
            int j = i - 1;
            int temp = arr[i];
            while (j >= 0 && temp < arr[j]) {
                arr[j + 1] = arr[j];
                j--;
                ;
            }
            arr[j + 1] = temp;
            System.out.println(": ");
            // Printing array after pass
            printExpenses(arr);
        }
    }
    static int binarySearchAscending(int[] array, int left, int right, int key) {
        if (left > right) {
          return -1;
        }

        int mid = (left + right) / 2;

        if (array[mid] == key) {
          return mid;
        }

        if (array[mid] > key) {
          return binarySearchAscending(array, left, mid - 1, key);
        }

        return binarySearchAscending(array, mid + 1, right, key);
      }


    static int binarySearchDescending(int[] array, int left, int right, int key) {
        if (left > right) {
          return -1;
        }

        int mid = (left + right) / 2;

        if (array[mid] == key) {
          return mid;
        }

        if (array[mid] > key) {
          return binarySearchDescending(array, mid + 1, right, key);
        }

        return binarySearchDescending(array, left, mid - 1, key);
      }
}

标签： javabinary-search

解决方案

您的问题出在这一行：

if (order == 1) {int ans = binarySearchAscending(userInput, 0, Size, value);//use the binary search ascending method

您希望上限为Size - 1而不是Size，如下所示：

if (order == 1) {int ans = binarySearchAscending(userInput, 0, Size-1, value);//use the binary search ascending method

您应该看到这适用于所有情况。您对binarySearchDescending的调用也存在同样的问题。

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