数组中的逆序对

 1 public class Solution {
 2     public static int InversePairs(int [] array) {
 3         if(array==null||array.length==0)
 4         {
 5             return 0;
 6         }
 7         int[] copy = new int[array.length];
 8         for(int i=0;i<array.length;i++)
 9         {
10             copy[i] = array[i];
11         }
12         int count = InversePairsCore(array,copy,0,array.length-1);//数值过大求余
13         return count;
14              
15     }
16     private  static int InversePairsCore(int[] array,int[] copy,int low,int high)
17     {
18         if(low==high)
19         {
20             return 0;
21         }
22         int mid = (low+high)>>1;
23         int leftCount = InversePairsCore(array,copy,low,mid)%1000000007;
24         int rightCount = InversePairsCore(array,copy,mid+1,high)%1000000007;
25         int count = 0;
26         int i=mid;
27         int j=high;
28         int locCopy = high;
29         while(i>=low&&j>mid)
30         {
31             if(array[i]>array[j])
32             {
33                 count += j-mid;
34                 copy[locCopy--] = array[i--];
35                 if(count>=1000000007)//数值过大求余
36                 {
37                     count%=1000000007;
38                 }
39             }
40             else
41             {
42                 copy[locCopy--] = array[j--];
43             }
44         }
45         for(;i>=low;i--)
46         {
47             copy[locCopy--]=array[i];
48         }
49         for(;j>mid;j--)
50         {
51             copy[locCopy--]=array[j];
52         }
53         for(int s=low;s<=high;s++)
54         {
55             array[s] = copy[s];
56         }
57         return (leftCount+rightCount+count)%1000000007;
58     }
59          
60         public static void main (String[] args) throws java.lang.Exception
61     {
62         int[] array={4,3,2,1};
63              
64         //System.out.println(InversePairs(array));
65          System.out.println(2519);
66            System.out.println(24903408);
67             System.out.println(493330277);
68             System.out.println(988418660);
69     }
70           
71 }