題目描述： 分析： 經典二分查詢演算法，實現出來很簡單。 程式碼：

#include<iostream>
#include<string>
#include<Windows.h>
#include<cstring>
#define MAXN 10010
using namespace std;
int main()
{
	int n, val;
	int a[MAXN];
	int st, en, mid;
	cin >> n;
	st = 1;en = n;
	for (int i = 1;i <= n;i++) cin >> a[i];
	cin >> val;
	while (st <= en)
	{
		mid = (st + en) >> 1;
		if (a[mid] == val) {
			cout << mid << endl;
			system("pause");
			return 0;
		}
		else if (a[mid] > val) {
			en = mid - 1;
		}
		else st = mid + 1;
	}
	cout << "-1" << endl;
	system("pause");
	return 0;
}