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import java.util.Arrays;public class Test2 {    public static void main(String[] args) {        int[] a = {1,3,5,6,7,8,9,10,12,18,19,20,100};        System.out.println(binarySearch(a, 9));        System.out.println(Arrays.binarySearch(a, 9));    }    public static int binarySearch(int[] a, int res){        int begin = 0;        int end = a.length - 1;        while(begin <= end){            int mid = (begin + end) / 2;            if(a[mid] > res){                begin = mid + 1;            }else if(a[mid] < res){                end = mid - 1;            }else{                return mid;            }        }        return -1;    }}

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