关于Robert Sedgewick和Kevin Wayne在“算法第4版”第115页上的练习1.2.9

public class Rank {
    public static int rank(int[] arr, int key) {
        int lo = 0;
        int hi = arr.length - 1;
        int count = 0;

        while (lo <= hi) {
            int mid = lo + (hi - lo) / 2;
            if (arr[mid] < key) {
                count = mid + 1;
                lo = mid + 1;
            } else if (arr[mid] > key) {
                hi = mid - 1;
            } else {
                hi = mid - 1;
            }
        }

        return count;
    }

    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int key = 5;
        int result = rank(arr, key);
        System.out.println("小于" + key + "的元素数量为：" + result);
    }
}