二分查找

#include <iostream>
using namespace std;

int a[20] = {0};

void init()
{
for (int i = 0; i < sizeof(a) / sizeof(int); ++i)
{
a[i] = 2 * i;
}
}

int binarysearch(int a1[], int begin, int end, int key)
{
while (begin <= end)
{
int mid = (begin + end) / 2;
if (key < a1[mid])
end = mid - 1;
else if (key > a1[mid])
begin = mid + 1;
else
return mid;
}
return -1;
}
int main()
{
init();
cout<<binarysearch(a,0,sizeof(a) / sizeof(int) - 1, 6)<<endl;
cout<<binarysearch(a,0,sizeof(a) / sizeof(int) - 1, 7)<<endl;
return 0;
}