Submission #861301

#	Time	Username	Problem	Language	Result	Execution time	Memory
861301		pedroslrey	Sorting (IOI15_sorting)	C++14	100 / 100	220 ms	20276 KiB

sorting

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

using namespace std;

bool check(int n, int xs[], int k, int ss1[], int ss2[], int ans1[] = nullptr, int ans2[] = nullptr) {
	vector<int> ideal(n), idealrev(n), ys(n), ysrev(n);
	for (int i = 0; i < n; ++i)
		ideal[i] = idealrev[i] = ysrev[ys[i] = xs[i]] = i;

	for (int i = k-1; i >= 0; --i) {
		swap(ideal[ss1[i]], ideal[ss2[i]]);
		swap(idealrev[ideal[ss1[i]]], idealrev[ideal[ss2[i]]]);
	}

	int lst = 0;
	for (int i = 0; i < k; ++i) {
		swap(ideal[ss1[i]], ideal[ss2[i]]);
		swap(idealrev[ideal[ss1[i]]], idealrev[ideal[ss2[i]]]);
		swap(ys[ss1[i]], ys[ss2[i]]);
		swap(ysrev[ys[ss1[i]]], ysrev[ys[ss2[i]]]);

		// cerr << "-> " << lst << " " << idealrev[lst] << " " << ysrev[lst] << "\n";
		while (lst < n && idealrev[lst] == ysrev[lst]) ++lst;
		if (lst < n) {
			int a = ysrev[lst], b = idealrev[lst]; 
			swap(ys[a], ys[b]);
			swap(ysrev[ys[a]], ysrev[ys[b]]);

			if (ans1 != nullptr) { ans1[i] = a; ans2[i] = b; }
		}
		else if (ans1 != nullptr) { ans1[i] = 0; ans2[i] = 0; }
	}

	for (int i = 0; i < n; ++i)
		if (ys[i] != i) return false;
	// cerr << k << "TRUE\n";
	return true;
}

int findSwapPairs(int n, int xs[], int m, int ss1[], int ss2[], int ans1[], int ans2[]) {
	int l = 0, r = m;
	while (l < r) {
		int mid = (l + r)/2;

		if (check(n, xs, mid, ss1, ss2)) r = mid;
		else l = mid + 1;
	}

	check(n, xs, r, ss1, ss2, ans1, ans2);
	return r;
}

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