二分查找

/**
 * @program: 
 * @description:
 * @author: Jay
 * @create: 2020-09-21 19:17
 **/
public class TwoSearch {
    /**
     * 不使用递归的二分查找
     * title:commonBinarySearch
     *
     * @param arr
     * @param key
     * @return 关键字位置
     */
    public static int commonBinarySearch(int[] arr, int key) {
        int low = 0;
        int high = arr.length - 1;
        int middle = 0;            //定义middle

        if (key < arr[low] || key > arr[high] || low > high) {
            return -1;
        }

        while (low <= high) {
            middle = (low + high) / 2;
            if (arr[middle] > key) {
                //比关键字大则关键字在左区域
                high = middle - 1;
            } else if (arr[middle] < key) {
                //比关键字小则关键字在右区域
                low = middle + 1;
            } else {
                return middle;
            }
        }

        return -1;        //最后仍然没有找到，则返回-1
    }

    public static void main(String[] args) {

        int[] arr = {1, 3, 5, 7, 9, 11};
        int key = 5;
        //int position = recursionBinarySearch(arr,key,0,arr.length - 1);

        int position = commonBinarySearch(arr, key);

        if (position == -1) {
            System.out.println("查找的是" + key + ",序列中没有该数！");
        } else {
            System.out.println("查找的是" + key + ",找到位置为：" + position);
        }

    }

}