二分查找时在给定已按升序排好序的n个元素a[0:n-1]， 用折半查找法在从这n个元素中找出一特定元素x，时间复杂性为O(logn)。
具体实现如下：
复制代码
//二分查找
static int binarySearch(int []a, int x, int n)
{
int left = 0,right = n-1;
int middle;
while (left <= right)
{
middle = (left+right)/2;
if (x == a[middle]) return middle;
if (x > a[middle]) left = middle + 1;
else right = middle - 1;
}
return -1;
}