JavaSE中你想看的例子——二分查找

        int[] arr = {1,2,3,54,2};
        System.out.println(search(arr, 2));
        //二分查找
        public static int search(int[] a, int num){
            int first = 0;
            int last = a.length;
            while(first <= last){
                int mid = (first + last)/2;
                if (a[mid] < num) {
                    first = mid + 1;
                }else if (a[mid] > num) {
                    last = mid - 1;
                }else {
                    return mid;
                }
            }
            return -1;
        }