线段树——Ultra-QuickSort

题目网址：http://acm.hust.edu.cn/vjudge/contest/view.action?cid=109331#problem/A

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

Sample Output

6

0

题意：输入n个数，相邻两个数可以交换位置进行从小到大排序，求最小交换次数。

解题思路：用线段树的思想将数组一半一半的划分成小的区间，最后划分为只有两个数的区间，这两个数进行比较交换位置，记录交换次数就。先进行前两个数的比较，然后扩大区间为（left，right），

可知（left，right）区间中，（left，center）和（center+1，right）区间里的数已经排好序，将（center+1，right）中的数一个一个与（left，center）中的数比较大小，用另一个数组记录
新的排序后的位置（相当于向前插入数），并记录交换次数。

#include <iostream>

#include <algorithm>

#include <cstring>

#include <cstdio>

#include <cstdlib>

using namespace std;

int a[];

long long num;

int temp[];

void Merge(int arr[], int left, int center, int right)

{

    int i=left;

    int j=center+;

    int k=;

    while (i<=center&&j<=right)

    {

        ///可知（left，right）区间中，（left，center）和（center+1，right）区间里的数已经排好序

        if (arr[i] > arr[j])

        {

            temp[k++] = arr[j++];///

            num+= center+-i;

        }

        else

            temp[k++] = arr[i++];///记录小的数，以便得到排序后新的序列；

    }

    while (i <= center) ///

        temp[k++] = arr[i++];

    while (j <= right)  ///这个和上个while语句两个while语句记录了原数组交换次序后的新的数组；

        temp[k++] = arr[j++];

    for (i = left, k = ; i <= right; i++, k++)///将array[]数组变为新的数组；

        arr[i] = temp[k];

}

void mergeSort(int arr[], int left, int right)

{

    if (left<right)

    {

        int center = (left + right) / ;

        mergeSort(arr, left, center);     ///

        mergeSort(arr, center + , right);///将数组划分为两个区间；

        Merge(arr, left, center, right);  ///将这个区间里的数进行排序；

    }

}

int main()

{

   int n;

   while(scanf("%d",&n)&&n)

   {

      num=;

      for(int i=;i<n;i++)

      scanf("%d",&a[i]);

      mergeSort(a,,n-);

      printf("%lld\n",num);

   }

}

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线段树——Ultra-QuickSort

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