Submission #129522

#	Time	Username	Problem	Language	Result	Execution time	Memory
129522		johutha	Sorting (IOI15_sorting)	C++14	100 / 100	186 ms	21988 KiB

sorting

#include "sorting.h"
#include <vector>
#include <iostream>

using namespace std;

int findSwapPairs(int n, int S[], int M, int X[], int Y[], int P[], int Q[]) {
	vector<int> perm(n);
	bool bc = true;
	for (int i = 0; i < n; i++)
	{
		perm[i] = S[i];
		if (perm[i] != i) bc = false;
	}
	if (bc) return 0;
	vector<int> b = perm;
	vector<int> beg = perm;
	for (int i = 0; i < n; i++)
	{
		swap(perm[X[i]], perm[Y[i]]);
	}
	vector<int> end = perm;
	int l = 0;
	int r = n;
	while (r - l > 1)
	{
		int m = (l + r)/2;
		vector<int> mv = beg;
		for (int i = l; i < m; i++)
		{
			swap(mv[X[i]], mv[Y[i]]);
		}
		
		vector<bool> v(n, false);
		int ctr = 0;
		for (int i = 0; i < n; i++)
		{
			if (v[i]) continue;
			v[i] = true;
			int cc = 0;
			int cr = i;
			while (mv[cr] != i)
			{
				cc++;
				cr = mv[cr];
				v[cr] = true;
			}
			ctr += cc;
		}

		if (ctr <= m)
		{
			r = m;
			end = mv;
		}
		else
		{
			l = m;
			beg = mv;
		}
	}

	vector<pair<int,int>> swp;
	perm = b;

	for (int i = 0; i < n; i++)
	{
		while (end[i] != i)
		{
			swp.push_back({end[i], end[end[i]]});
			swap(end[i], end[end[i]]);
		}
	}

	vector<int> revind(n);
	for (int i = 0; i < n; i++)
	{
		revind[perm[i]] = i;
	}

	for (int i = 0; i < r; i++)
	{
		swap(revind[perm[X[i]]], revind[perm[Y[i]]]);
		swap(perm[X[i]], perm[Y[i]]);
		if (i < swp.size())
		{
			Q[i] = revind[swp[i].first];
			P[i] = revind[swp[i].second];
			swap(revind[swp[i].first], revind[swp[i].second]);
			swap(perm[Q[i]], perm[P[i]]);
		}
		else
		{
			Q[i] = 0;
			P[i] = 0;
		}
	}

	return r;
}

Compilation message (stderr)

sorting.cpp: In function 'int findSwapPairs(int, int*, int, int*, int*, int*, int*)':
sorting.cpp:85:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (i < swp.size())
       ~~^~~~~~~~~~~~
sorting.cpp:7:39: 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