swustoj-1360: Ultra-QuickSort（归并排序）

杂

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

#include<stdio.h>
int a[500005],b[500005];
long long ans;
void merge(int m[],int temp[],int start,int mid,int end)
{
    int i=start,j=mid+1,cnt=start;
    while(i<=mid&&j<=end)
    {
        if(m[i]<=m[j])
            temp[cnt++]=m[i++];
        else
        {
            temp[cnt++]=m[j++];
            ans=ans+mid-i+1;
        }
    }
    while(i<=mid)
        temp[cnt++]=m[i++];
    while(j<=end)
        temp[cnt++]=m[j++];
    for(i=start;i<=end;i++)
        m[i]=temp[i];
}
void mergesort(int m[],int temp[],int start,int end)
{
    if(start==end)return;
    int mid=(start+end)/2;
    mergesort(m,temp,start,mid);
    mergesort(m,temp,mid+1,end);
    merge(m,temp,start,mid,end);
}
int main()
{
    int n,i;
    while(scanf("%d",&n),n)
    {
        ans=0;
        for(i=0;i<n;i++)
            scanf("%d",&a[i]);
        mergesort(a,b,0,n-1);
        printf("%lld\n",ans);
    }
    return 0;
}