Submission #769303

#	Time	Username	Problem	Language	Result	Execution time	Memory
769303		erekle	Arranging Shoes (IOI19_shoes)	C++17	100 / 100	56 ms	14860 KiB

shoes

#include "shoes.h"
#include <algorithm>
#include <vector>

using namespace std;

// Fenwick tree
void update(vector<int> &fenwick, int index, int value) {
	while (index < (int)fenwick.size()) {
		fenwick[index] += value;
		index += index & -index;
	}
}
int getSum(const vector<int> &fenwick, int index) {
	int sum = 0;
	while (index) {
		sum += fenwick[index];
		index -= index & -index;
	}
	return sum;
}
// Reverse fenwick tree for suffix sums
void updateR(vector<int> &fenwick, int index, int value) {
	update(fenwick, (int)fenwick.size()-index, value);
}
int getSumR(const vector<int> &fenwick, int index) {
	return getSum(fenwick, (int)fenwick.size()-index);
}

long long count_swaps(vector<int> s) {
	int n = (int)s.size() / 2;
	vector<vector<int>> nxt[2];
	nxt[0] = nxt[1] = vector<vector<int>>(1+n);
	for (int i = 2*n-1; i >= 0; --i) {
		if (s[i] < 0) nxt[0][-s[i]].push_back(i);
		else nxt[1][s[i]].push_back(i);
	}

	vector<int> fenwickMoved(1+2*n);
	vector<bool> paired(2*n);

	long long swaps = 0;
	for (int i = 0; i < 2*n; ++i) {
		if (paired[i]) continue;
		int v = abs(s[i]), side = s[i] > 0;
		int j = nxt[1-side][v].back();

		swaps += (j + getSumR(fenwickMoved, j+1)) - (i + getSumR(fenwickMoved, i+1));
		if (!side) --swaps; // do not need to swap with each other
		updateR(fenwickMoved, j+1, +1);
	
		paired[i] = true, paired[j] = true;
		nxt[0][v].pop_back(), nxt[1][v].pop_back();
	}
	return swaps;
}

• Subtask 1: 10 / 10
• Subtask 2: 20 / 20
• Subtask 3: 20 / 20
• Subtask 4: 15 / 15
• Subtask 5: 20 / 20
• Subtask 6: 15 / 15