Submission #722083

#	Time	Username	Problem	Language	Result	Execution time	Memory
722083		SlavicG	Alternating Current (BOI18_alternating)	C++17	0 / 100	17 ms	6108 KiB

alternating

#include "bits/stdc++.h"
using namespace std;
 
#define ll long long
 
#define          all(v)              v.begin(), v.end()
#define         rall(v)              v.rbegin(),v.rend()
 
#define            pb                push_back
#define          sz(a)               (int)a.size()

const int N = 1e5 + 10;
int t[4 * N], lazy[4 * N], n, m, ans[N], a[N], b[N];
vector<int> adj[N];
void push(int i, int l, int r) {
    if(!lazy[i]) return;
    t[i] += lazy[i];
    if(l != r) {
        lazy[2 * i] += lazy[i];
        lazy[2 * i + 1] += lazy[i];
    }
    lazy[i] = 0;
}
void modif(int i, int l, int r, int tl, int tr, int val) {
    push(i, l, r);
    if(l > tr || r < tl) return;
    if(l >= tl && r <= tr) {
        lazy[i] += val;
        push(i, l, r);
        return;
    }
    int mid = l + r >> 1;
    modif(2 * i, l, mid, tl, tr, val);
    modif(2 * i + 1, mid + 1, r, tl, tr, val);
    t[i] = min(t[2 * i], t[2 * i + 1]);
}
int query(int i, int l, int r, int tl, int tr) {
    push(i, l, r);
    if(l > tr || r < tl) return 1e9;
    if(l >= tl && r <= tr) return t[i];
    int mid = l + r >> 1;
    return min(query(2 * i, l, mid, tl, tr), query(2 * i + 1, mid + 1, r, tl, tr));
}
void modif(int l, int r, int val) {
    if(l <= r) modif(1, 1, n, l, r, val);
    else {
        modif(1, 1, n, l, n, val);
        modif(1, 1, n, 1, r, val);
    }
}
int query(int l, int r) {
    if(l <= r) return query(1, 1, n, l, r);
    else {
        return min(query(1, 1, n, l, n), query(1, 1, n, 1, r));
    }
}
bool dfs(int u) {
    for(int v: adj[u]) {
        if(ans[v] == 0) {
            ans[v] = -ans[u];
            if(!dfs(v)) return false;
        } else if(ans[v] == ans[u]) return false;
    }
    return true;
}
void solve() {
    cin >> n >> m;
    set<int> ongoing;
    vector<pair<int, int>> events;
    for(int i = 1; i <= m; ++i) {
        cin >> a[i] >> b[i];
        if(a[i] > b[i]) ongoing.insert(i);
        events.pb({a[i], i});
        events.pb({b[i] + 1, -i});
    }

    for(int i = 1, j = 0; i <= n; ++i) {
        while(j < sz(events) && events[j].first == i) {
            if(events[j].second < 0) ongoing.erase(-events[j].second);
            else ongoing.insert(events[j].second);
            ++j;
        }
        if(sz(ongoing) < 2) {
            cout << "impossible\n";
            return;
        }
        if(sz(ongoing) == 2) {
            int A = *ongoing.begin(), B = *++ongoing.begin();
            adj[A].pb(B);
            adj[B].pb(A);
        }
    }
    for(int i = 1; i <= m; ++i) {
        if(ans[i] == 0 && sz(adj[i])) {
            ans[i] = -1;
            if(!dfs(i)) {
                cout << "impossible\n";
                return;
            }
        }
    }
    for(int i = 1; i <= m; ++i) {
        if(ans[i] >= 0) modif(a[i], b[i], 1);
    }
    for(int i = 1; i <= m; ++i) {
        if(ans[i] == 0) {
            if(query(a[i], b[i]) >= 2) {
                ans[i] = -1;
                modif(a[i], b[i], -1);
            } else {
                ans[i] = 1;
            }
        }
    }
    for(int i = 1; i <= m; ++i) {
        cout << (ans[i] == -1 ? 0 : 1);
    }
}   
 
int32_t main() {
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t = 1;
    //cin >> t;
    while(t--) {
        solve();
    }
}

Compilation message (stderr)

alternating.cpp: In function 'void modif(int, int, int, int, int, int)':
alternating.cpp:32:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   32 |     int mid = l + r >> 1;
      |               ~~^~~
alternating.cpp: In function 'int query(int, int, int, int, int)':
alternating.cpp:41:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   41 |     int mid = l + r >> 1;
      |               ~~^~~

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