Ultra-QuickSort(归并排序求逆序对数)

Time Limit: 7000MS		Memory Limit: 65536K
Total Submissions: 34283		Accepted: 12295

Description

In this problem, you have to analyze a particular sorting algorithm. The algorithm processes a sequence of n distinct integers by swapping two adjacent sequence elements until the sequence is sorted in ascending order. For the input sequence 
9 1 0 5 4 ,
Ultra-QuickSort produces the output 
0 1 4 5 9 .
Your task is to determine how many swap operations Ultra-QuickSort needs to perform in order to sort a given input sequence.

Input

The input contains several test cases. Every test case begins with a line that contains a single integer n < 500,000 -- the length of the input sequence. Each of the the following n lines contains a single integer 0 ≤ a[i] ≤ 999,999,999, the i-th input sequence element. Input is terminated by a sequence of length n = 0. This sequence must not be processed.

Output

For every input sequence, your program prints a single line containing an integer number op, the minimum number of swap operations necessary to sort the given input sequence.

Sample Input

5
9
1
0
5
4
3
1
2
3
0

Sample Output

6
0

//归并排序模板，只加了一句 cnt += m-p;

 #include<stdio.h>
 #include<string.h>
 long long  cnt;
 int num[],tmp[];
 void merge_sort(int num[],int x, int y, int tmp[])
 {
     if(y-x > )
     {
         int m = x + (y-x)/;
         int p = x, q = m, i = x;
         merge_sort(num,x,m,tmp);
         merge_sort(num,m,y,tmp);
         while(p < m || q < y)
         {
             if(q >= y || (p < m && num[p] <= num[q]))
                 tmp[i++] = num[p++];
             else
             {
                 tmp[i++] = num[q++];
                 cnt += m-p;
             }
         }
         for(i = x; i < y; i++)
             num[i] = tmp[i];
     }
 }
 int main()
 {
     int n;
     while(~scanf("%d",&n) && n)
     {
         for(int i = ; i < n; i++)
             scanf("%d",&num[i]);
         cnt = ;
         merge_sort(num,,n,tmp);
         printf("%I64d\n",cnt);
     }
     return ;
 }