Submission #143208

#	Time	Username	Problem	Language	Result	Execution time	Memory
143208		mlyean00	Arranging Shoes (IOI19_shoes)	C++17	100 / 100	353 ms	140180 KiB

shoes

#include <bits/stdc++.h>

#include "shoes.h"

using namespace std;
using ll = long long;

int sgn(int x) {
    if (x == 0) return 0;
    return x > 0 ? 1 : -1;
}

ll count_inversions(vector<int>& v, int l, int r) {
    if (r - l == 1) return 0;
    int mid = (l + r) / 2;
    ll ans = count_inversions(v, l, mid) + count_inversions(v, mid, r);

    int l_ptr = l, r_ptr = mid;

    vector<int> m;
    m.reserve(r - l);

    while (l_ptr < mid || r_ptr < r) {
        if (l_ptr == mid) {
            m.push_back(v[r_ptr++]);
        } else if (r_ptr == r) {
            ans += r_ptr - mid;
            m.push_back(v[l_ptr++]);
        } else if (v[l_ptr] <= v[r_ptr]) {
            ans += r_ptr - mid;
            m.push_back(v[l_ptr++]);
        } else {
            m.push_back(v[r_ptr++]);
        }
    }

    copy(m.begin(), m.end(), v.begin() + l);

    return ans;
}

ll count_swaps(vector<int> s) {
    int n = s.size() / 2;

    vector<int> v {0};
    for (int x : s) {
        if (x > 0) v.push_back(x);
    }
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());

    for (int i = 0; i < 2 * n; ++i) {
        int k = sgn(s[i]);
        s[i] = k * (lower_bound(v.begin(), v.end(), abs(s[i])) - v.begin());
    }

    vector<int> t;

    vector<int> cnt(v.size());
    for (int i = 0; i < 2 * n; ++i) {
        int sz = abs(s[i]);
        if (cnt[sz] == 0 || sgn(s[i]) == sgn(cnt[sz])) {
            t.push_back(-sz);
            t.push_back(sz);
        }
        cnt[sz] += sgn(s[i]);
    }
    assert(t.size() == 2 * n);

    int offset = v.size() - 1;
    vector<stack<int>> st(2 * v.size() - 1);
    for (int i = 2 * n - 1; i >= 0; --i) {
        st[s[i] + offset].push(i);
    }

    vector<int> perm(2 * n);
    for (int i = 0; i < 2 * n; ++i) {
        perm[i] = st[t[i] + offset].top();
        st[t[i] + offset].pop();
    }

    return count_inversions(perm, 0, 2 * n);
}

Compilation message (stderr)

In file included from /usr/include/c++/7/cassert:44:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:33,
                 from shoes.cpp:1:
shoes.cpp: In function 'll count_swaps(std::vector<int>)':
shoes.cpp:68:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     assert(t.size() == 2 * n);
            ~~~~~~~~~^~~~~~~~

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