poj 2299 -- Ultra-QuickSort

Ultra-QuickSort

Time Limit: 7000MS		Memory Limit: 65536K
Total Submissions: 39538		Accepted: 14259

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

水题，与归并排序求逆序对是一个道理。

/*======================================================================
 *           Author :   kevin
 *         Filename :   Ultra-QuickSort.cpp
 *       Creat time :   2014-07-14 10:10
 *      Description :
========================================================================*/
#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <queue>
#include <cmath>
#define clr(a,b) memset(a,b,sizeof(a))
#define M 500005
using namespace std;
long long s[M],temp[M],cnt;
void mergearray(long long a[],int first,int mid,int last,long long temp[]){
    int i = first,j = mid + 1;
    int m = mid,  n = last;
    int k = 0;
    while(i <= m && j <= n){
        if(a[i] < a[j])
            temp[k++] = a[i++];
        else{
            temp[k++] = a[j++];
            cnt += mid-i+1;
        }
    }
    while(i <= m)
        temp[k++] = a[i++];
    while(j <= n)
        temp[k++] = a[j++];
    for(i = 0; i < k; i++)
        a[first+i] = temp[i];
}
void mergesort(long long a[],int first,int last,long long temp[])
{
    if(first < last){
        int mid = (first + last) / 2;
        mergesort(a,first,mid,temp);
        mergesort(a,mid+1,last,temp);
        mergearray(a,first,mid,last,temp);
    }
}
int main(int argc,char *argv[])
{
    int n;
    while(scanf("%d",&n)!=EOF && n){
        cnt = 0;
        for(int i = 0; i < n; i++){
            scanf("%lld",&s[i]);
        }
        mergesort(s,0,n-1,temp);
        printf("%lld\n",cnt);
    }
    return 0;
}