【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 };