Submission #374932

#	Time	Username	Problem	Language	Result	Execution time	Memory
374932		Alex_tz307	Arranging Shoes (IOI19_shoes)	C++17	45 / 100	143 ms	26976 KiB

shoes

#include <bits/stdc++.h>

using namespace std;
using int64 = long long;

vector<int> aib;

void update(int x, int N) {
    for(int i = x; i <= N; i += i & -i)
        ++aib[i];
}

int query(int x) {
    int ans = 0;
    for(int i = x; i > 0; i -= i & -i)
        ans += aib[i];
    return ans;
}

int64 count_swaps(vector<int> s) {
    int N = s.size();
    vector<vector<int>> from_s(N + 1);
    int add = N / 2;
    for(int i = 0; i < N; ++i)
        from_s[s[i] + add].emplace_back(i);
    vector<int> t, ptr(N + 1);
    for(int i = 0; i < N / 2; ++i) {
        int negative, positive;
        if(s[i] > 0)
            negative = add - s[i], positive = s[i] + add;
        else
            negative = s[i] + add, positive = add - s[i];
        t.emplace_back(from_s[negative][ptr[negative]++]);
        t.emplace_back(from_s[positive][ptr[positive]++]);
    }
    vector<vector<int>> from_t(N + 1);
    for(int i = 0; i < N; ++i)
        from_t[s[t[i]] + add].emplace_back(i);
    vector<int> perm(N + 1);
    int cnt = 0;
    for(int i = 0; i <= N; ++i)
        for(int j = 0; j < (int)from_s[i].size(); ++j) {
            int poz = from_s[i][j] + 1;
            perm[poz] = from_t[i][j] + 1;
        }
    int64 ans = 0;
    aib.resize(N + 1);
    for(int i = N; i > 0; --i) {
        ans += query(perm[i] - 1);
        update(perm[i], N);
    }
    return ans;
}

Compilation message (stderr)

shoes.cpp: In function 'int64 count_swaps(std::vector<int>)':
shoes.cpp:40:9: warning: unused variable 'cnt' [-Wunused-variable]
   40 |     int cnt = 0;
      |         ^~~

• Subtask 1: 10 / 10
• Subtask 2: 0 / 20
• Subtask 3: 20 / 20
• Subtask 4: 15 / 15
• Subtask 5: 0 / 20
• Subtask 6: 0 / 15