Submission #102713

#	Time	Username	Problem	Language	Result	Execution time	Memory
102713		wxh010910	Sorting (IOI15_sorting)	C++17	100 / 100	224 ms	18760 KiB

sorting

#include <bits/stdc++.h>
#include "sorting.h"

using namespace std;

int findSwapPairs(int N, int S[], int M, int X[], int Y[], int P[], int Q[]) {
  vector<bool> visit(N);
  vector<int> after(N);
  auto check = [&](int mid) {
    for (int i = 0; i < N; ++i) {
      after[i] = S[i];
      visit[i] = false;
    }
    for (int i = 0; i < mid; ++i) {
      swap(after[X[i]], after[Y[i]]);
    }
    int ans = 0;
    for (int i = 0; i < N; ++i) {
      if (!visit[i]) {
        for (int j = i; ; j = after[j]) {
          visit[j] = true;
          if (!visit[after[j]]) {
            P[ans] = i;
            Q[ans] = after[j];
            ++ans;
          } else {
            break;
          }
        }
      }
    }
    for (int i = ans; i < mid; ++i) {
      P[i] = Q[i] = 0;
    }
    return ans <= mid;
  };
  int l = 0, r = N;
  while (l < r) {
    int mid = (l + r) >> 1;
    if (check(mid)) {
      r = mid;
    } else {
      l = mid + 1;
    }
  }
  check(r);
  vector<int> pos(N);
  vector<int> to(N);
  for (int i = 0; i < N; ++i) {
    pos[i] = to[i] = i;
  }
  for (int i = r - 1; ~i; --i) {
    P[i] = to[P[i]];
    Q[i] = to[Q[i]];
    swap(pos[X[i]], pos[Y[i]]);
    to[pos[X[i]]] = X[i];
    to[pos[Y[i]]] = Y[i];
  }
  return r;
}

Compilation message (stderr)

sorting.cpp: In function 'int findSwapPairs(int, int*, int, int*, int*, int*, int*)':
sorting.cpp:6:39: warning: unused parameter 'M' [-Wunused-parameter]
 int findSwapPairs(int N, int S[], int M, int X[], int Y[], int P[], int Q[]) {
                                       ^

• Subtask 1: 8 / 8
• Subtask 2: 12 / 12
• Subtask 3: 16 / 16
• Subtask 4: 18 / 18
• Subtask 5: 20 / 20
• Subtask 6: 26 / 26