Submission #1519783

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Source Code Expand

//#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define IN(a, b, x) (a<=x&&x<b)
#define MP make_pair
#define PB push_back
const int INF = (1LL<<30);
const ll LLINF = (1LL<<60);
const double PI = 3.14159265359;
const double EPS = 1e-12;
const int MOD = 1000000007;
//#define int ll

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

VI aa, a, unzip(100010);
unordered_map<int, int> zip;
int n;
VI compress() {
  a = aa;
  sort(ALL(aa));
  aa.erase(unique(ALL(aa)), aa.end());
  REP(i, aa.size()) {
    zip[aa[i]] = i;
    unzip[i] = aa[i];
  }
  REP(i, a.size()) {
    a[i] = zip[a[i]];
  }
  return a;
}

int bit[100010], m = 100010;

//0からi-1番目までの和
int sum(int i) {
  i++;
  int s = 0;
  while(i > 0) {
    s += bit[i];
    i -= i&-i;
  }
  return s;
}

//i番目(0-index)にxを加える
void add(int i, int x) {
  i++;
  while(i <= m) {
    bit[i] += x;
    i += i&-i;
  }
}

signed main(void)
{
  cin >> n;
  REP(i, n) {
    int tmp;
    cin >> tmp;
    aa.PB(tmp);
  }
  compress();

  VI b, c;
  REP(i, n) {
    if(i%2) c.PB(a[i]);
    else b.PB(a[i]);
  }
  sort(ALL(b)); sort(ALL(c));
  // for(int i: b) cout << i << " "; cout << endl;
  // for(int i: c) cout << i << " "; cout << endl;

  VI ret;
  int i1 = 0, i2 = 0;
  REP(i, n) {
    if(i%2) ret.PB(c[i1++]);
    else ret.PB(b[i2++]);
  }

  // for(int i: ret) cout << i << " "; cout << endl;

  ll ans = 0;
  REP(j, n) {
    ans += j - sum(ret[j]);
    // cout << "j:" << j << " ans:" << ans << " " << sum(ret[j]) << endl;
    add(ret[j], 1);
  }
  cout << ans << endl;

  return 0;
}

Submission Info

Judge Result