折半查找

//二分查找的前提是有序的数。
public class BinarySearch {
    public static void main(String[] args) {
        int[] arr = {1, 2, 4, 5, 6, 8, 9, 10};
        System.out.println(binarySearch(arr, arr.length, 3));
    }

    /**
     *
     * @param arr 数组
     * @param arrlen 数组长度
     * @param x 要查找的数
     * @return 返回数所在位置下标
     */
    public static int binarySearch(int[] arr, int arrlen, int x) {
        int low, high, mid;
        low = 0;
        high = arrlen-1;//数组是从0开始的，所以需要-1
        while (low <= high) {
            mid = (low + high) / 2;
            if (arr[mid] == x)
                return mid;
            else if (arr[mid] > x)
                high = mid - 1;
            else
                low = mid + 1;
        }
        return -1;
    }
}
结果为-1