Leetcode 34: Search for a Range

Given an array of integers sorted in ascending order, 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].

 

 1 public class Solution {
 2     public int[] SearchRange(int[] nums, int target) {
 3         int[] result = {Int32.MaxValue, Int32.MinValue};
 4         
 5         BinarySearch(nums, target, 0, nums.Length - 1, true, result);
 6         BinarySearch(nums, target, 0, nums.Length - 1, false, result);
 7         
 8         result[0] = result[0] == Int32.MaxValue ? -1 : result[0];
 9         result[1] = result[1] == Int32.MinValue ? -1 : result[1];
10         
11         return result;
12     }
13     
14     private void BinarySearch(int[] nums, int target, int start, int end, bool up, int[] result)
15     {
16         if (start > end) return;
17         
18         if (start == end)
19         {
20             if (nums[start] == target)
21             {
22                 result[0] = Math.Min(result[0], start);
23                 result[1] = Math.Max(result[1], start);
24             }
25             
26             return;
27         }
28         
29         int mid = start + (end - start) / 2;
30         if (nums[mid] == target)
31         {
32             result[0] = Math.Min(result[0], mid);
33             result[1] = Math.Max(result[1], mid);
34 
35             if (up)
36             {
37                 BinarySearch(nums, target, mid + 1, end, up, result);
38             }
39             else
40             {
41                 BinarySearch(nums, target, start, mid - 1, up, result);
42             }
43         }
44         else if (nums[mid] < target)
45         {
46             BinarySearch(nums, target, mid + 1, end, up, result);
47         }
48         else
49         {
50             BinarySearch(nums, target, start, mid - 1, up, result);
51         }
52     }
53 }

 

posted @ 2017-11-06 02:55  逸朵  阅读(113)  评论(0)    收藏  举报