折半查找

class search
{
	public static void main(String[] args) {
		int[] arr = {1,10,20,28,45,90,100,200};
		System.out.println(search(arr, 1));
	}

	static int search(int[] arr, int key) {
		int max,min,mid;
		max = arr.length - 1;
		min = 0;
		mid = (max + min) / 2;
		while (arr[mid] != key) {
			if (arr[mid] > key) {
				max = mid - 1;
			} else if (arr[mid] < key) {
				min = mid + 1;
			} else {
				return mid;
			}

			mid = (max + min) / 2;

			if (max < min) {
				 return -1;

				// return -min-1;

				// 折半查找，没存在值，返回插入点，负数，是区别查找，-1 是因为有0的情况存在。  
			}

		}
		return mid;
	}

}