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【LeetCode 34】Search for a Range

时间:2015-07-19 16:21:34      阅读:79      评论:0      收藏:0      [点我收藏+]

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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 };

 

【LeetCode 34】Search for a Range

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原文地址:http://www.cnblogs.com/tjuloading/p/4658693.html

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