【LeetCode 34】Search for a Range

Given a sorted array of integers, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

For example,
Given [5, 7, 7, 8, 8, 10] and target value 8,
return [3, 4].

题意：

　　给定一个有序数组，其中可能包含一些重复数字，给定一个数字，求其第一次和最后一次出现的坐标，要求 O(log n)。

思路：

　　有序数组+ O(log n)，很显然二分搜索啦。

C++：

 1 class Solution {

 2 public:

 3 

 4     int Bsearch(vector<int>& nums, int len, int start, int end, int tar, bool flag)

 5     {

 6         if(start > end)

 7             return -1;

 8         

 9         int mid = (start + end) / 2;

10         

11         if(nums[mid] == tar)

12         {

13             if(flag)

14             {

15                 if((mid > 0 && nums[mid - 1] != tar) || mid == 0)

16                 {

17                     return mid;

18                 }

19                 else

20                 {

21                     return Bsearch(nums, len, start, mid - 1, tar, flag);

22                 }

23             }

24             else

25             {

26                 if((mid < len - 1 && nums[mid + 1] != tar) || mid == len - 1)

27                 {

28                     return mid;

29                 }

30                 else

31                 {

32                     return Bsearch(nums, len, mid + 1, end, tar, flag);

33                 }

34             }

35 

36         }

37         else if(nums[mid] < tar)

38         {

39             return Bsearch(nums, len, mid + 1, end, tar, flag);

40         }

41         else

42         {

43             return Bsearch(nums, len, start, mid - 1, tar, flag);

44         }

45     }

46 

47     vector<int> searchRange(vector<int>& nums, int target) {

48         

49         int len = nums.size();

50         vector<int> ret;

51         if(len == 0)

52             return ret;

53         

54         ret.push_back(Bsearch(nums, len, 0, len - 1, target, true));

55         ret.push_back(Bsearch(nums, len, 0, len - 1, target, false));

56         

57         return ret;

58     }

59 };