| Time Limit: 7000MS | Memory Limit: 65536K | |
| Total Submissions: 47235 | Accepted: 17258 |
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
Input
Output
Sample Input
5
9
1
0
5
4
3
1
2
3
0
Sample Output
6
0
Source
#include <cstdio>
#include <cstring>
#include <algorithm>
#define ll long long
using namespace std;
int const MAX = 500005;
int a[MAX], n;
ll ans;
void Merge(int l, int mid, int r)
{
int i = l, j = mid + 1;
while(i <= mid && j <= r)
{
if(a[i] <= a[j])
i ++;
else
{
j ++;
//因为左右区间都是有序的，因此a[i]>a[j]说明a[i]~a[mid]都大于a[j]
ans += mid - i + 1;
}
}
sort(a + l, a + r + 1);
return;
}
void Merge_sort(int l, int r)
{
if(l < r)
{
int mid = (l + r) / 2;
Merge_sort(l, mid);
Merge_sort(mid + 1, r);
Merge(l, mid, r);
}
return;
}
int main()
{
while(scanf("%d", &n) != EOF && n)
{
ans = 0;
for(int i = 0; i < n; i++)
scanf("%d", &a[i]);
Merge_sort(0, n - 1);
printf("%lld\n", ans);
}
}版权声明：本文为博主原创文章，未经博主允许不得转载。
POJ 2299 Ultra-QuickSort (归并排序求逆序数)
原文地址：http://blog.csdn.net/tc_to_top/article/details/46930961
