【剑指offer 面试题38】数字在排序数组中出现的次数

 1 #include <iostream>
 2 #include <vector>
 3 using namespace std;
 4 
 5 int GetFirstK(vector<int>& nums, int startpos, int endpos, int k)
 6 {
 7     if(startpos > endpos)
 8         return -1;
 9 
10     int mid = (startpos + endpos) / 2;
11 
12     if(nums[mid] == k)
13     {
14         if(mid == 0 || (mid > 0 && nums[mid - 1] != k))
15             return mid;
16         else
17             endpos = mid - 1;
18     }
19     else if(nums[mid] < k)
20     {
21         startpos = mid + 1;
22     }
23     else
24     {
25         endpos = mid - 1;
26     }
27 
28     return GetFirstK(nums, startpos, endpos, k);
29 }
30 
31 int GetLastK(vector<int>& nums, int startpos, int endpos, int k)
32 {
33     if(startpos > endpos)
34         return -1;
35 
36     int mid = (startpos + endpos) / 2;
37     int lastpos = nums.size() - 1;
38 
39     if(nums[mid] == k)
40     {
41         if(mid == lastpos || (mid < lastpos && nums[mid + 1] != k))
42             return mid;
43         else
44             startpos = mid + 1;
45     }
46     else if(nums[mid] < k)
47     {
48         startpos = mid + 1;
49     }
50     else
51     {
52         endpos = mid - 1;
53     }
54 
55     return GetLastK(nums, startpos, endpos, k);
56 }
57 
58 int main()
59 {
60     int a[10] = {1, 2, 3, 3, 3, 3, 3, 4, 4, 5};
61     vector<int> v(a, a +10);
62 
63     cout<<GetLastK(v, 0, 9, 4) - GetFirstK(v, 0, 9, 4) + 1<<endl;
64 }