Ultra-QuickSort

利用归并排序统计逆序数，利用归并求逆序在对子序列s1和s2在归并时（s1,s2已经排好序），若s1[i]>s2[j](逆序状况)，则逆序数加上s1.length-i,因为s1中i后面的数字对于s2[j]都是逆序的。

#include <stdio.h>
#include <stdlib.h>
int N;
int num[500001];
int tmp[500001];
__int64 count;
void Merge(int l,int mid,int r){
    int i=l,j=mid+1,k=0;
    while(i<=mid&&j<=r){
     if(num[i]>num[j]) {
        tmp[k++]=num[j++];
        count+=mid-i+1;
     } else
     {
         tmp[k++]=num[i++];
     }
    }
    while(i<=mid) tmp[k++]=num[i++];
     while(j<=r)  tmp[k++]=num[j++];

        for(i=0; i<k; i++)
        {
            num[l+i]=tmp[i];
        }
}
void Mergesort(int l,int r){
    int mid=(l+r)/2;
    if(l<r){
        Mergesort(l,mid);
        Mergesort(mid+1,r);
        Merge(l,mid,r);
    }
}
int main(void) {
    scanf("%d",&N);
    int i=0;
    while(N){
        for(i=0;i<N;i++){
            scanf("%d",&num[i]);
        }
        count=0;
        Mergesort(0,N-1);
        printf("%I64d 
",count);
        scanf("%d",&N);
    }



    return EXIT_SUCCESS;
}

附：

Time Limit: 7000MS		Memory Limit: 65536K
Total Submissions: 48082		Accepted: 17536

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