Submission #536687

#	Time	Username	Problem	Language	Result	Execution time	Memory
536687		OttoTheDino	Alternating Current (BOI18_alternating)	C++17	19 / 100	68 ms	16212 KiB

alternating

#include <bits/stdc++.h>
using namespace std;

#define rep(i,s,e)                  for (int i = s; i <= e; ++i)
#define rrep(i,s,e)                 for (int i = s; i >= e; --i)
#define pb                          push_back
#define pf                          push_front
#define fi                          first
#define se                          second
#define all(a)                      a.begin(), a.end()
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int n, m; cin >>n >> m;
    vector<ii> v[2*n];
    set<ii> st;
    set<pair<ii,int>> s;

    rep (i,0,m-1) {
        int a, b; cin >> a >> b;
        a--, b--;
        if (b<a || a==0) {
            s.insert({{b,a},i});
        }
        else {
            v[a].pb({b,i});
        }
    }

    if (s.size()<2) {
        cout << "impossible\n";
        return 0;
    }

    int l = (*s.begin()).fi.fi, x = (*s.begin()).fi.se-1, idl = (*s.begin()).se;
    if (x==-1) x = n-1;
    s.erase(s.begin());
    int r = (*s.begin()).fi.fi, y = (*s.begin()).fi.se-1, idr = (*s.begin()).se;
    if (y==-1) y = n-1;
    s.erase(s.begin());

    if (y<x) {
        swap (l, r);
        swap (y, x);
        swap (idl, idr);
    }

    bool suc = 1, ans[m+1] = {};

    ans[idr] = 1;

    for (auto sth : s) {
        st.insert({sth.fi.fi, sth.se});
    }

    rep (i,0,n-1) {
        for (ii bi : v[i]) st.insert(bi);
        if (i>l && i<=x) {
            if (st.size()>1 && (*prev(st.end(),2)).fi>=i) {
                l = (*prev(st.end(),2)).fi;
                st.erase(prev(st.end(),2));
            }
            else if (st.size() && (*prev(st.end())).fi>=i) {
                l = (*prev(st.end())).fi;
                st.erase(prev(st.end()));
            }
            else {
                suc = 0;
                break;
            }
        }
        if (i>r && i<=y) {
            if (st.size() && (*st.rbegin()).fi>=i) {
                ans[(*st.rbegin()).se] = 1;
                r = (*st.rbegin()).fi;
                st.erase(--st.end());
            }
            else {
                suc = 0;
                break;
            }
        }
    }

    if (!suc) {
        cout << "impossible\n";
    }
    else {
        rep (i,0,m-1) cout << ans[i];
        cout << "\n";
    }

    return 0;
}

• Subtask 1: 0 / 13
• Subtask 2: 0 / 20
• Subtask 3: 0 / 22
• Subtask 4: 19 / 19
• Subtask 5: 0 / 26