【歸併排序+逆序數】poj-2299 Ultra-QuickSort

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題目描述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.

 

輸入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.

 

輸出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.

 

範例輸入

59105431230

 

範例輸出

60


就是讓你從小到大排序，每次只能交換相鄰元素，求最小次數

#include <bits/stdc++.h>#define ll long long#define INF 0x3f3f3f3fusing namespace std;const int M=500005;int L[M/2+2],R[M/2+2];int t[M];ll ans;int n;void mergearr(int A[],int left,int mid,int right){    int i=left,j=mid+1;    int k=left;    while(i<=mid&&j<=right)    {        if(A[i]<=A[j])            t[k++]=A[i++];        else{            t[k++]=A[j++];            ans+=mid-i+1;        }    }    while(i<=mid)        t[k++]=A[i++];    while(j<=right)        t[k++]=A[j++];    for(int i=left;i<=right;i++)        A[i]=t[i];}void mergeSort(int A[],int left,int right){    if(left<right)    {        int mid=(left+right)/2;        mergeSort(A,left,mid);        mergeSort(A,mid+1,right);        mergearr(A,left,mid,right);    }}int main(){    int A[M];    int n,i;    while(scanf("%d",&n)&&n!=0)    {        ans=0;        for(int i=1;i<=n;i++)        {            scanf("%d",&A[i]);        }         mergeSort(A,1,n);        printf("%lld\n",ans);    }    return 0;}

 

【歸併排序+逆序數】poj-2299 Ultra-QuickSort