剑指Offer36 数字在排序数组中出现的次数

Posted 2020-08-06 Juntaran

 1 /*************************************************************************
 2     > File Name: 36_NumberOfKey.c
 3     > Author: Juntaran
 4     > Mail: [email protected]
 5     > Created Time: 2016年09月03日 星期六 09时32分10秒
 6  ************************************************************************/
 7 
 8 #include <stdio.h>
 9 
10 // 寻找第一个Key的下标
11 int GetFirstKey(int* nums, int length, int key, int left, int right)
12 {
13     if (nums==NULL || length<=0 || left>right)
14         return -1;
15     
16     int middle = (left + right) / 2;
17     if (key == nums[middle])
18     {
19         if ((middle>0 && nums[middle-1]!=key) || middle==0)
20             return middle;
21         else
22             right = middle - 1;
23     }
24     else if (key > nums[middle])
25         left = middle + 1;
26     else
27         right = middle - 1;
28     
29     return GetFirstKey(nums, length, key, left, right);
30 }
31 
32 // 寻找最后一个Key的下标
33 int GetLastKey(int* nums, int length, int key, int left, int right)
34 {
35     if (nums==NULL || length<=0 || left>right)
36         return -1;
37     
38     int middle = (left + right) / 2;
39     if (key == nums[middle])
40     {
41         if ((middle>0 && nums[middle+1]!=key && middle<length) || middle==length-1)
42             return middle;
43         else
44             left = middle + 1;
45     }
46     else if (key > nums[middle])
47         left = middle + 1;
48     else
49         right = middle - 1;
50     
51     return GetLastKey(nums, length, key, left, right);
52 }
53 
54 int GetNumberOfKey(int* nums, int length, int key)
55 {
56     int count = 0;
57     if (nums==NULL || length<=0)
58         return 0;
59     
60     int first = GetFirstKey(nums, length, key, 0, length-1);
61     int last  = GetLastKey( nums, length, key, 0, length-1);
62     
63     if (first>=0 && last>=0)
64         count = last - first + 1;
65     
66     printf("count is %d\n", count);
67     return count;
68 }
69 
70 int main()
71 {
72     int nums[] = {1, 2, 3, 3, 3, 3, 4, 5};
73     int length = 8;
74     int key = 3;
75     
76     GetNumberOfKey(nums, length, key);
77 }