import java.util.Arrays;

public class BinarySearch {
    public static void main(String[] args) {
        int[] arr = {30,20,50,10,80,9,7,12,100,40,8};
        //二分法适用于已经排好序的数组
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
        //返回搜索的值所在的数组的下标，假如不存在，则返回-1
        System.out.println(myBinarySearch(arr,20));
    }

    private static int myBinarySearch(int[] arr, int value) {
        int low = 0;
        int high = arr.length-1;
        while(low<=high) {
            int middle = (low+high)/2;
            if(value == arr[middle]) {
                return middle;
            } else if(value > arr[middle]) {
                low = middle + 1;
            } else if(value < arr[middle]) {
                high = middle -1;
            }
        }
        return -1;
    }
}