Given a sorted array of strings which is interspersed with empty strings, write a method to find the location of a given string.
Example: find “ball” in [“at”, “”, “”, “”, “ball”, “”, “”, “car”, “”, “”, “dad”, “”, “”] will return 4
Example: find “ballcar” in [“at”, “”, “”, “”, “”, “ball”, “car”, “”, “”, “dad”, “”, “”] will return -1

可以直接遍歷一遍查詢，但是O(n)不夠好；

因為已經排好序，所以binary search.

每次t=mid，然後遇到空格就t++直到大於high。

1.如果t>high,說明[mid, high]這一段都是空格，就需要在[low, mid-1]去找。

2.如果在[mid, t]這一段裡面找到x，那麼就返回。

3.如果在[mid, t]第一個不是空格的string > x, 說明x要在[low, mid-1]去找。

3.如果在[mid, t]第一個不是空格的string < x, 說明x要在[t+1, high]去找。

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

int search(string s[], int low, int high, string x)
{
    if(x=="")
        return -1;

    while(low<=high)
    {
        int mid=low+(high-low)/2;
        int t=mid;
        while(s[t]=="" && t<=high)
            t++;
        if(t>high)
        {
            high=mid-1;
        }
        else
        {
            if(s[t]==x)
                return t;
            else if(s[t]>x)
                high=mid-1;
            else
                low=t+1;
        }
    }
    return -1;
}
int main()
{
    string s[13] =
    {
        "at", "", "", "", "ball", "", "", "car", "", "", "dad", "", ""
    };
    cout<<search(s, 0, 12, "ball")<<endl;
    return 0;
}