代码

int binary_search(const unsigned *a, int n, unsigned x)
{
	static int ans=-1,nx;
	register unsigned l=0,r=n-1,mid;
	if(ans!=-1)
	{
		if(x==nx)return ans;
		if(x<nx)r=ans-1;
		else l=ans+1;
	}
	while(l<=r)
	{
		mid=(l+r)>>1;
		if(a[mid]==x)
		{
			nx=x;
			return ans=mid;
		}
		if(a[mid]<x)
		{
			l=mid+1;
		}
		else
		{
			r=mid-1;
		}
	}
	return l;
}

评测结果