第四篇排序算法|二分查找

public class BinarySearchTest2 {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20};
        int key = 12;
        int search = binarySearch(arr, key);
        System.out.println("search = " + search);
    }

    /**
     * @param arr 待查找数组元素
     * @param key 待查找元素
     * @return 元素在数组中的下标（index），找不到返回-1
     */
    public static int binarySearch(int[] arr, int key) {
        if (arr == null) {
            return -1;
        }
        int low = 0;
        int high = arr.length - 1;
        while (low <= high) {
            int mid = low + (high - low) / 2;
            if (key == arr[mid]) {
                return mid;
            } else if (key > arr[mid]) {
                low = mid + 1;
            } else if (key < arr[mid]) {
                high = mid - 1;
            }
        }
        return -1;
    }
}