package com.sxt.arraytest2;

/*

 * 二分查找 前提：有序

 */

public class TestBinarySearch {

    public static void main(String[] args) {

        //待查找序列

        int[] arr = {1,3,5,7,9,13};

        //待查目标

        int ele = 13;

        BSearch(arr,ele);

    }

    private static void BSearch(int[] arr, int ele) {

        //若存在存入index 否则index为初始值-1

        int index = -1;

        //开始的下标

        int start = 0;

        //结束的下标

        int end = arr.length-1;

        while(start <= end){//循环条件

            int mid = (start + end)/2;

            if(arr[mid] == ele){

                index = mid;

                break;//若找到 跳出循环！！

            }else if(arr[mid] > ele){

                end = mid - 1;

            }else{

                start = mid + 1;

            }

        }

        if(index == -1){

            System.out.println("不存在元素"+ele);

        }else{

            System.out.println("该元素的下标："+index);

        }

    }

}