1 /*************************************************************************
2 > File Name: 34_InversePairsInArray.c
3 > Author: Juntaran
4 > Mail: JuntaranMail@gmail.com
5 > Created Time: 2016年09月02日 星期五 20时05分05秒
6 ************************************************************************/
7
8 #include <stdio.h>
9 #include <malloc.h>
10
11 int InversePairsCore(int* nums, int* copy, int left, int right)
12 {
13 if (left == right)
14 {
15 copy[left] = copy[right];
16 return 0;
17 }
18 int newlength = (right - left) / 2;
19
20 // 递归
21 int leftCount = InversePairsCore(copy, nums, left, left+newlength);
22 int rightCount = InversePairsCore(copy, nums, left+newlength+1, right);
23
24 // i初始化为前半段最后一个数字下标
25 int i = left + newlength;
26 // j初始化为后半段最后一个数字下标
27 int j = right;
28
29 int indexCopy = right;
30 int count = 0;
31
32 while (i>=left && j>=left+newlength+1)
33 {
34 if (nums[i] > nums[j])
35 {
36 copy[indexCopy--] = nums[i--];
37 count += j - left - newlength;
38 }
39 else
40 {
41 copy[indexCopy--] = nums[j--];
42 }
43 }
44
45 for (i; i >= left; --i)
46 copy[indexCopy--] = nums[i];
47 for (j; j>=left+newlength+1; --j)
48 copy[indexCopy--] = nums[j];
49
50 return leftCount + rightCount + count;
51 }
52
53 int InversePairs(int* nums, int length)
54 {
55 if (nums==NULL || length<=0)
56 return -1;
57
58 int* copy = (int*)malloc(sizeof(int)*length);
59 for (int i = 0; i < length; ++i)
60 copy[i] = nums[i];
61
62 int count = InversePairsCore(nums, copy, 0, length-1);
63 delete[] copy;
64
65 return count;
66 }
67
68 int main()
69 {
70 int nums[] = {7,5,6,4};
71 int length = 4;
72 int ret = InversePairs(nums, length);
73 printf("%d\n", ret);
74 }
