Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

#include <iostream>
#include <cstdio>
using namespace std;

int f[60600];

int main()
{
    int n,x,ans=0;
    cin >> n;
    while (n--)
    {
        scanf("%d",&x);
        for (int i=x+1;i<=60000;i+=i&-i) ans+=f[i];
        for (int i=x;i;i-=i&-i) f[i]++;
    }
    cout << ans << endl;
}

Code mẫu của happyboy99x

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main implements Runnable {
    private static final int MAXVAL = 60000;
    private int tree[] = new int[MAXVAL+5], a[], n;

    public void run() {
        try {
            BufferedReader inp = new BufferedReader(new InputStreamReader(System.in));
            a = new int[n = Integer.parseInt(inp.readLine())];
            for( int i = 0; i < n; update(1, a[i++] = Integer.parseInt(inp.readLine())));
            int res = 0;
            for( int i = 0; i < n; i++ ) {
                res += read(a[i]-1);
                update(-1, a[i]);
            }
            System.out.println(res);
            inp.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void update( int val, int idx ) {
        for(;idx <= MAXVAL; idx += (idx & -idx)) tree[idx] += val;
    }

    private int read( int idx ) {
        int sum = 0;
        for(; idx > 0; idx -= (idx & -idx)) sum += tree[idx];
        return sum;
    }

    public static void main(String argv[]) {
        new Main().run();
    }
}

Code mẫu của ladpro98

#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <climits>
#include <cstdlib>
#include <ctime>
#include <memory.h>
#include <cassert>
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define REP(i, a, b) for(int i = (a); i <=(b); i++)
#define FORD(i, a, b) for(int i = (a); i > (b); i--)
#define REPD(i, a, b) for(int i = (a); i >=(b); i--)
#define SZ(a) (int((a).size()))
#define ALL(a) (a).begin(), (a).end()
#define PB push_back
#define MP make_pair
#define LL long long
#define LD long double
#define II pair<int, int>
#define X first
#define Y second
#define VI vector<int>
const int N = 60006;
using namespace std;
int a[N], tmp[N];
int n;

int cal(int l, int r) {
    if (l == r) return 0;
    int mid = l + r >> 1;
    int ans = cal(l, mid) + cal(mid + 1, r);
    int i = l, j = mid + 1, m = 0, last = 0, cnt = 0;
    while (i <= mid && j <= r) {
        if (a[i] <= a[j]) {
            tmp[m++] = a[i];
            if (a[i++] != last) ans += cnt;
        }
        else {
            tmp[m++] = a[j];
            last = a[j++]; cnt++;
        }
    }
    while (i <= mid) tmp[m++] = a[i], ans += (a[i++] != last) * cnt;
    while (j <= r) tmp[m++] = a[j++];
    FOR(i, 0, m) a[l + i] = tmp[i];
    return ans;
}


int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    cin >> n;
    FOR(i, 0, n) cin >> a[i];
    cout << cal(0, n - 1) << endl;
    return 0;
}

Code mẫu của RR

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <iomanip>
#include <bitset>
#include <complex>

#define FOR(i,a,b) for(int i = a; i <= b; ++i)
#define FORD(i,a,b) for(int i = a; i >= b; --i)
#define REP(i,a) for(int i = 0; i < a; ++i)
#define MP make_pair
#define PB push_back

using namespace std;

int n, a[60111], bit[60111];

#define _(x) ((x) & (-(x)))

inline void update(int k) {
    while (k <= 60000) {
        bit[k]++;
        k += _(k);
    }
}

inline int get(int x) {
    int res = 0;
    while (x > 0) {
        res += bit[x];
        x -= _(x);
    }
    return res;
}

int main() {
    scanf("%d", &n);
    FOR(i,1,n) scanf("%d", &a[i]);
    int res = 0;
    FORD(i,n,1) {
        res += get(a[i]-1);
        update(a[i]);
    }
    cout << res;
    return 0;
}

Code mẫu của hieult

#include <cstdio>
#include <cstring>
//#include <conio.h>
#define Max 111111
#define du 66666

using namespace std;

long long dem[du+10],a[Max],kq=0;

void update(int u){
     while(u<=60000){
          dem[u]++;
          u+=u&-u; 
     }
}

long long tinh(int u){
     long long r = 0;
     while(u>0){
          //printf("%d\n",u);
          r+=dem[u];
          u-=u&-u;
     }
     return r;
}

int main(){
    // freopen("NKINV.in","r",stdin);
     int n,L,R;
     memset(dem,0,sizeof(dem));
     scanf("%d",&n);
     a[0] = 0;
     for(int i = 1;i<=n;i++){
          scanf("%lld",&a[i]);
     }
     for(int i = n;i>=1;i--){
          kq+=tinh(a[i]-1);
          update(a[i]);
     }
     printf("%lld",kq);
// getch();
}

Code mẫu của ll931110

{$MODE DELPHI}
Program NKINV;
Const
  input  = '';
  output = '';
  maxn = 60000;
Var
  a: array[1..maxn] of integer;
  n: integer;
  res: integer;

Procedure update(v: integer);
Begin
  While v >= 1 do
    Begin
      inc(a[v]);
      v:= v - (v and (-v));
    End;
End;

Function calc(v: integer): integer;
Var
  t: integer;
Begin
  t:= 0;

  While v <= maxn do
    Begin
      t:= t + a[v];
      v:= v + (v and (-v));
    End;

  calc:= t;
End;

Procedure solve;
Var
  f: text;
  i,x: integer;
Begin
  Assign(f, input);
    Reset(f);

  res:= 0;
  Read(f, n);
  Fillchar(a, sizeof(a), 0);

  For i:= 1 to n do
    Begin
      Read(f, x);
      res:= res + calc(x);
      update(x - 1);
    End;

  Close(f);

  Assign(f, output);
    Rewrite(f);
    Writeln(f, res);
  Close(f);
End;

Begin
  solve;
End.

Code mẫu của skyvn97

#include<bits/stdc++.h>
#define MAX   60060
#define FOR(i,a,b) for (int i=(a),_b=(b);i<=_b;i=i+1)
using namespace std;
int a[MAX],b[MAX],cnt[MAX],n;
void init(void) {
    scanf("%d",&n);
    FOR(i,1,n) scanf("%d",&a[i]);
}
void process(void) {
    while (true) {
        bool allZero=true;
        FOR(i,1,n) if (a[i]>0) allZero=false;
        if (allZero) break;
        memset(cnt,0,sizeof cnt);
        FOR(i,1,n) {
            if (a[i]&1) cnt[a[i]]++;
            else b[i]+=cnt[a[i]+1];
            a[i]>>=1;
        }
    }
    long long res=0;
    FOR(i,1,n) res+=b[i];
    cout<<res<<endl;
}
int main(void) {
    init();
    process();
    return 0;
}

Code mẫu của khuc_tuan

import java.io.*;
import java.util.*;

public class Main {
    static int n, result;
    static int[] a, b;

    static void tim(int l,int r) {
        if(l==r) return;
        int m = (l+r) / 2;
        tim( l, m);
        tim( m+1, r);
        int st = m;
        for(int i=l;i<=m;++i) {
            while(st<r && a[st+1]<a[i]) ++st;
            result += st - m;
        }
        int st2 = l;
        st = m+1;
        for(int i=l;i<=r;++i) {
            if(st2>m) b[i] = a[st++];
            else if(st>r) b[i] = a[st2++];
            else if(a[st]<a[st2]) b[i] = a[st++];
            else b[i] = a[st2++];
        }
        for(int i=l;i<=r;++i) a[i] = b[i];
    }

    public static void main(String[] args) throws Exception {
        BufferedReader kb = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(kb.readLine());
        a = new int[n];
        b = new int[n];
        for(int i=0;i<n;++i) a[i] = Integer.parseInt(kb.readLine());
        result = 0;
        tim( 0, n-1);
        System.out.println(result);
    }
}