学步园

#include <iostream>
#include <cassert>
using namespace std;

int search(string a[], int lhs, int rhs, string val)
{
	string nil = " ";
	if(val == nil) return -1;
	while(lhs < rhs)
	{
		int mid = (lhs + rhs) >> 1;
	
		while(a[mid] == nil && mid < rhs)
			mid++;	
			
		if(a[mid] == val)
			return mid;
		if(mid >= rhs)
			rhs = mid - 1;
		else
		{
			if(val < a[mid])
			rhs = mid - 1;
			else
			lhs = mid + 1;
		}	
	}
	return -1;
}

int main(void)
{
	string a[] = {
 		 "at", " ", " ", " ", "ball", " ", " ", "car", " ", " ", "dad", " ", " " 
	};
	
/*
	for(int i = 0; i < 13; ++i)
		cout << a[i] << endl;*/
	
	cout << search(a, 0, 13, "ballcar") << endl;
	
	return 0;
}