二分法算法查找的实现

二分法检索（binary search）又称折半检索

package com.yqq.app11;

import java.util.Arrays;

/**
 * @Author yqq
 * @Date 2021/11/20 17:55
 * @Version 1.0
 */
public class TestBinarySearch {
    public static void main(String[] args) {
        int[] values = {20,12,8,50,30,100,80,9,7,40,10};
        //要查找的数
        int serachValue = 10;
        //二分查找之前一定要对数组元素排序
        Arrays.sort(values);
        System.out.println(Arrays.toString(values));
        System.out.println(serachValue+"元素索引："+binarySearch(values,serachValue));
    }

    private static int binarySearch(int[] values, int serachValue) {
        int startIndex = 0;
        int endIndex = values.length - 1;
        while (startIndex < endIndex){
            int middle = (startIndex + endIndex)/2;
            if(serachValue == values[middle])
                return middle;//返回查询到的索引位置
            if(serachValue > values[middle])
                startIndex = middle + 1;
            if(serachValue < values[middle])
                endIndex = middle - 1;
        }
        return -1;//循环完毕，说明没找到，返回-1
    }
}

[7, 8, 9, 10, 12, 20, 30, 40, 50, 80, 100]
10元素索引：3