Uva 11858 - Frosh Week

 // Header file begin
#include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<string>
#include<vector>
#include<cmath>
#include<cctype>
#include<sstream>
#include<set>
#include<list>
#include<stack>
#include<utility>
#include<queue>
#include<algorithm>
#include<cstdlib>
/// End
//..........
/// Macro
#define sf scanf
#define pf printf
#define lp1(i,n) for(i=0;i<n;i++)
#define lp2(i,n) for(i=1;i<=n;i++)
#define mem(c,v) memset(c,v,sizeof(c))
#define cp(a) cout<<" "<<a<<" "
#define nl puts("")
#define sq(x) ((x)*(x))
#define all(x) x.begin(),x.end()
#define reall(x) x.rbegin(),x.rend()
#define sz size()
#define gc getchar()
#define pb push_back
#define freader freopen("input.txt","r",stdin)
/// End.........

/// Size
#define mx7 20000100
#define mx6 1500000
#define mx5 100005
#define mx4 1000000
#define inf 1<<30                                           //infinity value
#define eps 1e-9
#define mx (65540)
#define mod 1000000007
#define pi acos(-1.0)

/// Macros for Graph

#define white 1
#define gray 2
#define black 3
#define nil 0

using namespace std;
/***************/

/// typedef

typedef long long LL;
typedef long L;
typedef unsigned long long ull;
typedef unsigned long ul;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef vector<int>vi;
typedef vector<long long> vll;
typedef vector<long>vl;
typedef vector<char>vch;
typedef vector<string>vs;
typedef map<int,int>mpii;
typedef map<int,bool>mpbi;
typedef map<long,bool>mpbl;
typedef map<long long,bool>mpbll;
typedef map<char,int>mpci;
typedef map<char,bool>mpbc;
typedef map<string,int>mpsi;
typedef map<long long,long long>mpll;

/// template

template<class T> T gcd(T a, T b ) {return b<=0?a:gcd(b,a%b);}
template<class T> T large(T a, T b ) {return a>b?a:b;}
template<class T> T small(T a, T b ) {return a<b?a:b;}
template<class T> T diffrnce(T a, T b) {return a-b<0?b-a:a-b;}

LL arr[mx4+5],n_swp,i,j,k;

void build_merge(LL p, LL q, LL r)
{
    LL n1 = q-p+1;
    LL n2 = r-q;

    vll left,right;

    for(i=0;i<n1;i++)
    {
        //left[i] = arr[p+i];
        left.push_back(arr[p+i]);
    }

    for(j=0;j<n2;j++)
    {
        //right[j] = arr[q+j+1];
        right.push_back(arr[q+j+1]);
    }

    //left[n1]=1000000000;
    //right[n2]=1000000000;
    left.push_back(1000000000);
    right.push_back(1000000000);

    LL x=0,y=0;

    for(k=p;k<=r;k++)
    {
        if(left[x] <= right[y])
        {
            arr[k] = left[x];
            x++;
        }

        else
        {
            arr[k] = right[y];
            y++;
            n_swp = (n_swp+n1)-x;
        }
    }
}

void merge_sort(LL p, LL r)
{
    if(p < r)
    {
        LL q = (int)floor((p+r) / 2.00);
        merge_sort(p,q);
        merge_sort(q+1,r);
        build_merge(p,q,r);
    }
}

int main()
{
    LL n;
    while(~sf("%lld",&n))
    {
        for(LL i=0;i<n;i++)
        {
            sf("%lld",&arr[i]);
        }

        n_swp=0;

        merge_sort(0,n-1);
        //for(LL i=0;i<n;i++)cout<<arr[i] << " ";
        pf("%lld\n",n_swp);
    }

    return 0;
}