2299 Poj Ultra-QuickSort(归并排序求逆序数)
2015-06-27 23:01
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Ultra-QuickSort
DescriptionIn 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.InputThe 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.OutputFor 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
Time Limit: 7000MS | Memory Limit: 65536K | |
Total Submissions: 46926 | Accepted: 17131 |
5 9 1 0 5 4 3 1 2 3 0Sample Output
6 0
#include<cstdio>#include<cstring>#include<iostream>using namespace std;int a[500010],b[500010];long long ans;void mer(int s,int mid,int e){ int i=s,j=mid+1,k=0; while(i<=mid&&j<=e) { if(a[i]>a[j]) //一定是看小的a[i]是否>a[j],成立的话从i到mid 的a[i]也是一定大于a[j]. { ans+=mid-i+1; b[k++]=a[j++]; } else b[k++]=a[i++]; } while(i<=mid) b[k++]=a[i++]; while(j<=e) b[k++]=a[j++]; for(i=s,k=0;i<=e;i++,k++) a[i]=b[k];}void fen(int s,int e){ if(s<e) { int mid=(s+e)/2; fen(s,mid);//分两部分不断递归 fen(mid+1,e); mer(s,mid,e); }}int main(){ int n,m,i,j; ios::sync_with_stdio(false); while(cin>>n&&n) { ans=0; for(i=0;i<n;i++) { cin>>a[i]; } fen(0,n-1); cout<<ans<<endl; } return 0;}
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