Java实现二分查找

如果要实现二分查找，那么被查找的数列一定是有序的。这里有对升序和降序数列的二分查找。

package exer;

import java.util.Scanner;


public class BinarySearch {
    static Scanner scan = new Scanner(System.in);
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[] arrNumber = new int[5];
        System.out.println("请输入五个有序(升序或降序)的值:");
        for (int i = 0; i < 5; i++) {
            arrNumber[i] = in.nextInt();
        }

        System.out.println("请输入您要查找的值：");
        int target = scan.nextInt();
        int start = 0, end = arrNumber.length - 1;
        //数列升序时
        int middle;
        if(arrNumber[start] < arrNumber[end] ) {
            while (start <= end) {
                middle = (start + end) / 2;
                if (arrNumber[middle] < target) start = middle + 1;
                if (arrNumber[middle] > target) end = middle;
                if (arrNumber[middle] == target) {
                    System.out.println("目标元素的索引为 ： " + middle);
                    return;
                }
            }
            System.out.println("您输入的元素不存在！");
        }else {//数列降序时
            while (start <= end) {
                middle = (start + end) / 2;
                if (arrNumber[middle] < target) start = middle - 1;
                if (arrNumber[middle] > target) end = middle + 1;
                if (arrNumber[middle] == target) {
                    System.out.println("目标元素的索引为 ： " + middle);
                    return;
                }
            }
            System.out.println("您输入的元素不存在！");
        }

    }

}