常用基础算法

1. 二分法
   //示例算法输出的是下标

#include 
using namespace std;
template
int BinarySearch(Type a[],const Type& x,int n){
   int left, right, mid;
   left = 0;
   right = n - 1;
   while(left <= right){
   	mid = (left + right) / 2;
   	if(x == a[mid])
   		return mid;
   	if(x < a[mid])
   		right = mid - 1;
   	else
   		left = mid + 1;
   }
   return -1;	
}
int main(){
   int n, x;
   cin >> n >> x;
   int a[n];
   for(int i = 0; i < n; i++)
   cin >> a[i];
   cout << BinarySearch(a, x, n);  
}

输入样例：

5 2
1 2 3 4 5

输出样例：

1