POJ_2299 Ultra-QuickSort [merge sort]

Question link: http://poj.org/problem? Id = 2299

Calculate the minimum number of exchanges in the sorting process

This problem is solved using the merge sort grouping algorithm.

Code:

#include <iostream>#include <cstdio>#include <cstring>#define N 500001using namespace std;int a[N];int temp[N];long long ans;void merge(int *a,int start,int mid,int end,int *temp){    int ai=start;    int bi=mid+1;    int k=0;    while (ai<=mid&&bi<=end)    {        if(a[ai]<=a[bi])            temp[k++]=a[ai++];        else        {            temp[k++]=a[bi++];            ans+=(mid-ai+1);        }    }    while (ai<=mid)        temp[k++]=a[ai++];    while (bi<=end)        temp[k++]=a[bi++];    for(int i=0;i<=end-start;i++)    {        a[start+i]=temp[i];    }}void merge_array(int *a,int start,int end){    if(start<end)    {        int mid=(start+end)/2;        merge_array(a,start,mid);        merge_array(a,mid+1,end);        merge(a,start,mid,end,temp);    }}int main(){    int n;    scanf("%d",&n);    while(n)    {        memset(a,0,sizeof(a));        ans=0;        for(int i=0;i<n;i++)            scanf("%d",&a[i]);        merge_array(a,0,n-1);        printf("%I64d\n",ans);        scanf("%d",&n);    }    return 0;}