[CareerCup] 11.5 Search Array with Empty Strings 搜尋含有空字串的陣列
阿新 • • 發佈：2018-12-27
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
這道題給了我們一個有序的字串陣列，但是在中間加入了很多空字串，讓我們來查詢一個給定字串。如果沒有這些空字串，那麼我們用二分查詢法很容易搜尋，但是這些空字串就有很大的干擾作用。那麼我們要在原有的二分查詢法上做修改，類似的修改二分查詢法的裡有 Search in Rotated Sorted Array 在旋轉有序陣列中搜索和Search in Rotated Sorted Array II 在旋轉有序陣列中搜索之二。這道題我們的思路是，查詢中間的字串，如果是空字串，那麼我們用二分查詢法來找周圍最近的非空字串，然後把mid移到飛空字串的位置，繼續二分查詢。相當於二分查詢中又嵌套了一個二分查詢，參見程式碼如下：
class Solution { public: 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; } };