Submission #3725021

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Source Code Expand

#include <bits/stdc++.h>
#define int long long
#define uint unsigned int
#define rep(i, a, n) for (int i = a; i < n; i++)
#define all(a) (a).begin(), (a).end()
#define sz(a) (a).size()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define dump(x) cerr << #x << " = " << (x) << endl;
#define dumpi(i, x) cerr << string((i), ' ') << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
using namespace std;
using pii = pair<int, int>;
constexpr int MOD = 1000000007;
constexpr int INF = 1LL << 30;
constexpr double EPS = 1e-10;

struct BIT {
  int n;
  vector<int> bit;
  BIT() {}
  BIT(int n, int e = 0) {
    build(n, e);
  }
  void build(int n_, int e) {
    n = n_ + 1;
    bit.resize(n, e);
  }
  void add(int k, int x) {
    while (k <= n) {
      bit[k] += x;
      k += k & -k;
    }
  }
  int sum(int k) {
    int r = 0;
    while (k > 0) {
      r += bit[k];
      k -= k & -k;
    }
    return r;
  }
  int &operator[](int i) {
    return bit[i];
  }
};

int N;
int B[100010], RB[100010];
BIT bitL, bitR;
int L[100010], R[100010];
int pos = -1;

signed main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  
  cin >> N;
  rep(i, 0, N) {
    cin >> B[i];
    if (B[i] == N) pos = i;
    RB[i] = B[i];
  }
  reverse(RB, RB+N);
  bitL.build(N, 0);
  bitR.build(N, 0);

  rep(i, 0, N) {
    if (i != pos) {
      L[i] = (i - (i > pos)) - bitL.sum(B[i]);
      bitL.add(B[i], 1);
    }
    if (i != N-pos-1) {
      R[i] = (i - (i > N-pos-1)) - bitR.sum(RB[i]);
      bitR.add(RB[i], 1);
    }
    if (i > 0) {
      L[i] += L[i-1];
      R[i] += R[i-1];
    }
  }
  reverse(R, R+N);
  rep(i, 0, N) {
    cerr << R[i] << " \n"[i+1==N];
  }
  int ans = INF;
  rep(i, 0, N) {
    int sum = abs(pos - i);
    if (pos < i) {
      sum += L[i];
      if (i+1 < N) sum += R[i+1];
    } else if (i < pos) {
      sum += R[i];
      if (i > 0) sum += L[i-1];
    } else {
      if (i+1 < N) sum += R[i+1];
      if (i > 0) sum += L[i-1];
    }
    ans = min(ans, sum);
  }
  cout << ans << endl;

  return 0;
}

Submission Info

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