Submission #1215583

#	Time	Username	Problem	Language	Result	Execution time	Memory
1215583		adaawf	Alternating Current (BOI18_alternating)	C++20	0 / 100	3093 ms	12096 KiB

alternating

#include <bits/stdc++.h>
using namespace std;
struct CUR {
    int x, y, num;
} a[100005], b[100005];
bool cmp(CUR aa, CUR bb) {
    return aa.x < bb.x;
}
vector<int> gg[200005];
vector<CUR> v;
int f[200005], res[100005], d[100005];
int main() {
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        cin >> a[i].x >> a[i].y;
        if (a[i].y + 1 == a[i].x) a[i] = {1, n};
        if (a[i].y < a[i].x) a[i].y += n;
        a[i].num = i;
        b[i] = a[i];
    }
    sort(a + 1, a + m + 1, cmp);
    int ma = 0, h = 0;
    for (int i = 1; i <= m; i++) {
        if (a[i].y <= ma) {
            d[a[i].num] = h;
        }
        else {
            v.push_back(a[i]);
            ma = a[i].y;
            h = a[i].num;
        }
    }
    if (v.size() % 2 == 0) {
        for (int i = 0; i < v.size(); i++) {
            int h = i % 2;
            res[v[i].num] = h;
        }
        for (int i = 1; i <= m; i++) {
            if (d[i]) res[i] = (res[d[i]] ^ 1);
            for (int j = b[i].x; j <= b[i].y; j++) {
                f[j] |= (1 << res[i]);
            }
        }
        for (int i = 1; i <= n; i++) {
            if ((f[i] | f[i + n]) != 3) {
                cout << "impossible";
                return 0;
            }
        }
    }
    else {
        for (int k = 0; k < v.size(); k++) {
            for (int i = 0; i < v.size(); i++) res[v[i].num] = 0;
            int h = k;
            while (1) {
                if ((k + 1) % v.size() == h) break;
                res[v[h].num] = 1;
                h += 2; h %= v.size();
            }
            for (int i = 1; i <= n * 2; i++) gg[i].clear();
            for (int i = 1; i <= m; i++) {
                if (d[i]) res[i] = (res[d[i]] ^ 1);
                gg[b[i].x].push_back(res[i] + 1);
                gg[b[i].y + 1].push_back(-(res[i] + 1));
            }
            int x = 0, y = 0;
            for (int i = 1; i <= n * 2; i++) {
                for (int w : gg[i]) {
                    if (w == 1) x++;
                    else if (w == 2) y++;
                    else if (w == -1) x--;
                    else y--;
                }
                f[i] = 0;
                if (x) f[i] |= 1;
                if (y) f[i] |= 2;
            }
            int flag = 0;
            for (int i = 1; i <= n; i++) {
                if ((f[i] | f[i + n]) != 3) {
                    flag = 1;
                    break;
                }
            }
            if (flag == 0) {
                for (int i = 1; i <= m; i++) cout << res[i];
                return 0;
            }
        }
        cout << "impossible";
        return 0;
    }
    for (int i = 1; i <= m; i++) cout << res[i];
}

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