Submission #774061

#	Time	Username	Problem	Language	Result	Execution time	Memory
774061		_martynas	Arranging Shoes (IOI19_shoes)	C++14	100 / 100	65 ms	16424 KiB

shoes

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

using namespace std;

using ll = long long;

ll count_swaps(vector<int> s) {
    int n = s.size()/2;
    vector<ll> fen(2*n+1);
    auto add = [&](int i, int x) {
        i++;
        while(i <= 2*n) {
            fen[i] += x;
            i += i&(-i);
        }
    };
    auto get = [&](int i) {
        i++;
        ll sum = 0;
        while(i) {
            sum += fen[i];
            i -= i&(-i);
        }
        return sum;
    };
    for(int i = 0; i < 2*n; i++) {
        add(i, 1);
    }
    vector<int> to(2*n, -1);
    vector<vector<int>> where(2*n+3);
    for(int i = 0; i < 2*n; i++) {
        where[s[i]+n].push_back(i);
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < where[i].size(); j++) {
            int a = where[i][j], b = where[abs(i-n)+n][j];
            if(a > b) swap(a, b);
            to[a] = b;
        }
    }
    ll ans = 0;
    for(int i = 0; i < 2*n; i++) {
        if(to[i] == -1) continue;
        int prev = ans;
        if(s[i] > 0) ans++;
        add(i, -1); add(to[i], -1);
        ans += get(to[i])-get(i);
    }
	return ans;
}

Compilation message (stderr)

shoes.cpp: In function 'll count_swaps(std::vector<int>)':
shoes.cpp:36:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |         for(int j = 0; j < where[i].size(); j++) {
      |                        ~~^~~~~~~~~~~~~~~~~
shoes.cpp:45:13: warning: unused variable 'prev' [-Wunused-variable]
   45 |         int prev = ans;
      |             ^~~~

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