poj-2299 Ultra—QuickSort（归并排序求逆序数）

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

Output

Sample Input

5
9 1 0 5 4
3
1 2 3
0

Sample Output

6
0

思路：

      归并排序求逆序数，用作模版

代码：

#include <stdio.h>
#define lld I64d
#define LL __int64
#define N 1000050

LL num[N];
LL temp[N];  // 归并排序的辅助数组
LL count = 0;

void Merge(LL * array, int first, int middle, int last)
{
	int i = first, j = middle + 1, cur = 0;
	while(i <= middle && j <= last){
		if(array[i] < array[j])
			temp[cur ++] = array[i ++];
		else{
			temp[cur ++] = array[j ++];
			count += middle - i + 1;
		}
	}
	while(i <= middle)
		temp[cur ++] = array[i ++];
	while(j <= last)
		temp[cur ++] = array[j ++];

	for (int k = 0; k < cur; k ++)
		array[first ++] = temp[k];
}

void MergeSort(LL *array, int first, int last)
{
	if (first == last)
		return ;
	
	int middle = first + (last - first) / 2;
	MergeSort(array, first, middle);
	MergeSort(array, middle+1, last);
	Merge(array, first, middle, last);
}

int main()
{
	int n, i;
	while(scanf("%d", &n), n){
		count = 0;
		for(i = 0; i < n; i ++)
			scanf("%lld", &num[i]);
		MergeSort(num, 0, n - 1);
	/*	for(i = 0; i < n; i ++)
			printf("%lld ", num[i]);
		printf("\n"); */
		printf("%lld\n", count);
	}

	return 0;
}

poj-2299 Ultra—QuickSort（归并排序求逆序数）,布布扣,bubuko.com

poj-2299 Ultra—QuickSort（归并排序求逆序数）

原文：http://blog.csdn.net/tbl_123/article/details/25335741