Submission #1058648

#	Time	Username	Problem	Language	Result	Execution time	Memory
1058648		otarius	Alternating Current (BOI18_alternating)	C++17	100 / 100	82 ms	18512 KiB

alternating

#include <bits/stdc++.h>
#include <bits/extc++.h>
using namespace __gnu_pbds;
using namespace std;
 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#define ff first
#define sc second
#define pb push_back
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define ull unsigned long long
#define all(x) (x).begin(),(x).end()
 
// #define int long long
// #define int unsigned long long
 
// #define ordered_set(T) tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>
// #define ordered_multiset(T) tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>
 
void open_file(string filename) {
    freopen((filename + ".in").c_str(), "r", stdin);
    freopen((filename + ".out").c_str(), "w", stdout);
}
 
// const ll mod = 1e9 + 7;
// const ll mod = 998244353;
 
const ll inf = 1e9;
const ll biginf = 1e18;
const int maxN = 1e5 + 25;
 
int par[maxN];
vector<int> g[maxN];
void make_set() {
    for (int i = 0; i <= maxN; i++) par[i] = i;
}
int find_set(int v) {
    if (v == par[v])
        return v;
    return par[v] = find_set(par[v]);
}
void union_set(int x, int y) {
    x = find_set(x);
    y = find_set(y);
    if (x != y) par[y] = x;
}
 
struct segtree {
    int t[4 * maxN], lazy[4 * maxN], n;
    void init(int _n) {
        n = _n;
        for (int i = 0; i < 4 * maxN; i++)
            t[i] = lazy[i] = 0;
    }
    
    void prop(int v, int tl, int tr) {
        if (!lazy[v]) return;
        t[v] += lazy[v];
        if (tl != tr) {
            lazy[2 * v] += lazy[v];
            lazy[2 * v + 1] += lazy[v];
        } lazy[v] = 0;
    }
    
    void update(int v, int tl, int tr, int l, int r, int val) {
        prop(v, tl, tr);
        if (r < tl || tr < l) return;
        if (l <= tl && tr <= r) {
            lazy[v] += val;
            prop(v, tl, tr);
            return;
        } int tm = (tl + tr) / 2;
        update(2 * v, tl, tm, l, r, val);
        update(2 * v + 1, tm + 1, tr, l, r, val);
        t[v] = min(t[2 * v], t[2 * v + 1]);
    }
    
    int query(int v, int tl, int tr, int l, int r) {
        prop(v, tl, tr);
        if (l > r) return -inf;
        if (tl == l && tr == r)
            return t[v];
        int tm = (tl + tr) / 2;
        return min(query(2 * v, tl, tm, l, min(r, tm)),
                   query(2 * v + 1, tm + 1, tr, max(l, tm + 1), r));
    }
    
    void update(int l, int r, int val) {
        if (r > n) r -= n;
        if (l <= r) {
            update(1, 1, n, l, r, val);
        }
        else {
            update(1, 1, n, l, n, val);
            update(1, 1, n, 1, r, val);
        }
    }
    
    int eval() {
        return query(1, 1, n, 1, n);
    }
} seg[2];
bool check() {
    return (seg[0].eval() > 0 && seg[1].eval() > 0);
}
 
struct line {
    int x, y, id, cl, clr;
    line() {
        
    }
    line(int _x, int _y, int _id) {
        x = _x; y = _y; id = _id; cl = clr = -1;
    }
    bool operator<(const line &p) {
        return make_pair(x, -y) < make_pair(p.x, -p.y);
    }
} arr[maxN];
bool comp(line a, line b) {
    return a.id < b.id;
}
 
vector<line> good;
int n, m, mx, mxi, cld[maxN];
void elim() {
    deque<line> dq;
    sort(arr + 1, arr + m + 1);
    for (int i = 1; i <= m; i++) {
        if (dq.empty() || dq.back().y < arr[i].y) dq.push_back(arr[i]);
        else cld[arr[i].id] = dq.back().id;
    } while (dq.size() && dq.front().y <= mx) {
        cld[dq.front().id] = mxi; dq.pop_front();
    } for (line x : dq) good.pb(x);
    for (int i = 1; i <= m; i++)
        if (cld[arr[i].id]) arr[i].cl = cld[arr[i].id];
    make_set();
    for (int i = 1; i <= m; i++)
        if (arr[i].cl != -1) union_set(arr[i].cl, arr[i].id);
    for (int i = 1; i <= m; i++) {
        if (arr[i].cl != -1) {
            arr[i].cl = find_set(arr[i].cl);
            g[arr[i].cl].pb(arr[i].id);
        } else g[arr[i].id].pb(arr[i].id);
    }
}
void even() {
    for (int i = 0; i < good.size(); i++)
        arr[good[i].id].clr = i % 2;
    for (int i = 1; i <= m; i++)
        if (arr[i].clr == -1) arr[i].clr = (arr[arr[i].cl].clr ^ 1);
    for (int i = 1; i <= m; i++) {
        seg[arr[i].clr].update(arr[i].x, arr[i].y, 1);
    }
    if (check()) {
        for (int i = 1; i <= m; i++)
            cout << arr[i].clr;
    } else {
        cout << "impossible";
    } exit(0);
}
void odd() {
    for (int i = 0; i < good.size(); i++)
        arr[good[i].id].clr = i % 2;
    for (int i = 1; i <= m; i++)
        if (arr[i].clr == -1) arr[i].clr = (arr[arr[i].cl].clr ^ 1);
    for (int i = 1; i <= m; i++)
        seg[arr[i].clr].update(arr[i].x, arr[i].y, 1);
    if (check()) {
        for (int i = 1; i <= m; i++)
            cout << arr[i].clr;
        exit(0);
    } for (int i = 0; i < good.size(); i++) {
        for (int j : g[good[i].id]) {
            seg[arr[j].clr].update(arr[j].x, arr[j].y, -1);
            arr[j].clr ^= 1;
            seg[arr[j].clr].update(arr[j].x, arr[j].y, 1);
        } if (check()) {
            for (int j = 1; j <= m; j++)
                cout << arr[j].clr;
            exit(0);
        }
    } cout << "impossible";
    exit(0);
}
void solve() {
    cin >> n >> m;
    seg[0].init(n); seg[1].init(n);
    for (int i = 1; i <= m; i++) {
        int l, r; cin >> l >> r;
        if (l > r) {
            if (mx < r) {
                mx = r; mxi = i;
            } r += n;
        } arr[i] = {l, r, i};
    } elim();
    sort(arr + 1, arr + m + 1, comp);
    if (good.size() % 2 == 0) even();
    else odd();
}
int32_t main() { 
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
        cout << '\n';
    }
    return 0;
}

Compilation message (stderr)

alternating.cpp: In function 'void even()':
alternating.cpp:152:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<line>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  152 |     for (int i = 0; i < good.size(); i++)
      |                     ~~^~~~~~~~~~~~~
alternating.cpp: In function 'void odd()':
alternating.cpp:167:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<line>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  167 |     for (int i = 0; i < good.size(); i++)
      |                     ~~^~~~~~~~~~~~~
alternating.cpp:177:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<line>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  177 |     } for (int i = 0; i < good.size(); i++) {
      |                       ~~^~~~~~~~~~~~~
alternating.cpp: In function 'void open_file(std::string)':
alternating.cpp:26:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   26 |     freopen((filename + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp:27:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   27 |     freopen((filename + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
alternating.cpp: In function 'void make_set()':
alternating.cpp:40:44: warning: iteration 100025 invokes undefined behavior [-Waggressive-loop-optimizations]
   40 |     for (int i = 0; i <= maxN; i++) par[i] = i;
      |                                     ~~~~~~~^~~
alternating.cpp:40:23: note: within this loop
   40 |     for (int i = 0; i <= maxN; i++) par[i] = i;
      |                     ~~^~~~~~~

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