[CareerCup] 11.5 Search Array with Empty Strings 搜索含有空字符串的数组 - Grandyang - 博客园

[CareerCup] 11.5 Search Array with Empty Strings 搜索含有空字符串的数组 - Grandyang - 博客园
11.5 Given a sorted array of strings which is interspersed with empty strings, write a method to find the location of a given string.
 EXAMPLE
 Input: find "ball" in {"at", "", "", "", "ball", "", "", "car", "", "", "dad", "", ""}
 Output: 4

这道题给了我们一个有序的字符串数组，但是在中间加入了很多空字符串，让我们来查找一个给定字符串。如果没有这些空字符串，那么我们用二分查找法很容易搜索，但是这些空字符串就有很大的干扰作用。那么我们要在原有的二分查找法上做修改，类似的修改二分查找法的里有Search in Rotated Sorted Array 在旋转有序数组中搜索和Search in Rotated Sorted Array II 在旋转有序数组中搜索之二。这道题我们的思路是，查找中间的字符串，如果是空字符串，那么我们用二分查找法来找周围最近的非空字符串，然后把mid移到飞空字符串的位置，继续二分查找。相当于二分查找中又嵌套了一个二分查找
Use ordinary binary search, but when you hit an empty string, advance to the next nonempty

string; if there is no next non-empty string, search the left half.

Also: http://xiaochongzhang.me/blog/?p=553

    int search(vector<string> strings, string str) {
        int first = 0, last = strings.size() - 1;
        while (first <= last) {
            int mid = first + (last - first) / 2;
            if (strings[mid].empty()) {
                int left = mid - 1, right = mid + 1;
                while (true) {
                    if (left < first && right > last) return -1;
                    else if (right <= last && !strings[right].empty()) {
                        mid = right; break;
                    }
                    else if (left >= first && !strings[left].empty()) {
                        mid = left; break;
                    }
                    ++right;
                    --left;
                }
            }
            int res = strings[mid].compare(str);
            if (res == 0) return mid;
            else if (res < 0) first = mid + 1;
            else last = mid - 1;
        }    
        return -1;
    }

http://xiaochongzhang.me/blog/?p=553

int findStrHelper(int begin, int end, vector<string> strings, string target_str)

{

    while(begin <= end)

    {

        while(begin <= end&&strings[end]=="")

            --end;

        if(begin > end)

            return -1;

        int mid = begin+(end-begin)/2;

        while(strings[mid] == "")

            ++mid;

        if(strings[mid] == target_str)

            return mid;

        if(strings[mid] < target_str)

            begin = mid+1;

        else if(strings[mid] > target_str)

            end = mid-1;

    }

    return -1;

}

 

//--------------------<11.5 find array with interspersed with empty strings>---------------------

int findStr(vector<string> strings, string target_str)

{

    if(strings.size() == 0||target_str.size() == 0)

        return -1;

    if(target_str == "")

    {

        for(int i = 0; i < strings.size(); ++i)

        {

            if(strings[i] == "")

                return i;

        }

        return -1;

    }

    return findStrHelper(0,strings.size()-1, strings, target_str);

 

}

http://adatechlife.blogspot.com/2013/08/find-string.html
https://adaguo.wordpress.com/2013/08/19/find-string/

int findstr(string *str, string s, int begin, int end) {

    if(end < begin) return -1;

    int mid = (begin + end) / 2;

    if(str[mid] == s) return mid;

    if(str[mid] == "") {

        int left = findstr(str, s, begin, mid-1);

        if(left != -1) return left;

        else return findstr(str, s, mid+1, end);

    } else if(str[mid] > s) {

        return findstr(str, s, begin, mid-1);

    } else return findstr(str, s, mid+1, end);

}

https://github.com/1094401996/CareerCup/blob/master/Chapter11/src/elevendot5/FindString.java
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