Submission #636447

#	Time	Username	Problem	Language	Result	Execution time	Memory
636447		borisAngelov	Arranging Shoes (IOI19_shoes)	C++14	100 / 100	69 ms	12712 KiB

shoes

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

using namespace std;

const int MAXN = 200005;

int n;

vector<pair<int, int>> same_size[MAXN];
vector<pair<int, int>> matchings;

struct FenwickTree {
    int fenwick[MAXN];

    void update(int pos, int val) {
        while (pos < 2 * n) {
            fenwick[pos] += val;
            pos += (pos & (-pos));
        }
    }

    int query(int pos) {
        int result = 0;

        while (pos > 0) {
            result += fenwick[pos];
            pos -= (pos & (-pos));
        }

        return result;
    }
};
FenwickTree Fenwick;

long long count_swaps(std::vector<int> shoes) {
    n = int(shoes.size()) / 2;

    for (int i = 0; i < 2 * n; i++) {
        same_size[abs(shoes[i])].push_back({shoes[i], i});
    }

    long long ans = 0;

    for (int i = 1; i <= n; i++) {
        sort(same_size[i].begin(), same_size[i].end());

        for (int j = 0; j < int(same_size[i].size()) / 2; j++) {
            int l = same_size[i][j].second;
            int r = same_size[i][j + int(same_size[i].size()) / 2].second;

            if (l > r) {
                swap(l, r);
                ans++;
            }

            matchings.push_back({l + 1, r + 1});
        }
    }

    sort(matchings.begin(), matchings.end());

    for (int i = 1; i <= 2 * n; i++) Fenwick.update(i, 1);

    for (int i = 0; i < matchings.size(); i++) {
        int l = matchings[i].first;
        int r = matchings[i].second;

        if (r - l > 1) ans += Fenwick.query(r - 1) - Fenwick.query(l);

        Fenwick.update(l, -1);
        Fenwick.update(r, -1);
    }

    return ans;
}

Compilation message (stderr)

shoes.cpp: In function 'long long int count_swaps(std::vector<int>)':
shoes.cpp:65:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   65 |     for (int i = 0; i < matchings.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~~~~~

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