Submission #1047951

#	Time	Username	Problem	Language	Result	Execution time	Memory
1047951		PurpleCrayon	Sprinklers (CEOI24_sprinklers)	C++17	26 / 100	145 ms	6992 KiB

Main

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

#define sz(v) int(v.size())
#define ar array
typedef long long ll;
const int N = 1e5+10, MOD = 1e9+7;
const int INF = 2e9+10;

void solve() {
    int n, m; cin >> n >> m;
    vector<int> a(n); for (auto& x : a) cin >> x;
    vector<int> b(m); for (auto& x : b) cin >> x;

    vector<string> build(n + 1);
    auto can = [&](int x) {
        vector<int> dp(n+1);
        auto upd = [&](int i, int me, string c) {
            if (dp[i] <= me) {
                dp[i] = me;
                build[i] = c;
            }
        };

        for (int i = 0; i < n; i++) {
            // dp[i+1] = max(dp[i+1], dp[i]);
            upd(i+1, dp[i], "L");

            if (dp[i] >= m) continue;
            int need = b[dp[i]];
            if (a[i] - x <= need && need <= a[i]) {
                int cur = upper_bound(b.begin(), b.end(), a[i]) - b.begin();
                upd(i+1, cur, "L");
                // dp[i+1] = max(dp[i+1], cur);
            }

            if (a[i] <= need && need <= a[i] + x) {
                int cur = upper_bound(b.begin(), b.end(), a[i] + x) - b.begin();
                upd(i+1, cur, "R");
                // dp[i+1] = max(dp[i+1], cur);
            }

            if (i < n-1 && a[i+1] <= a[i] + x) {
                if (a[i+1] - x <= need && need <= a[i] + x) {
                    int cur = upper_bound(b.begin(), b.end(), a[i] + x) - b.begin();
                    upd(i+2, cur, "RL");
                    // dp[i+2] = max(dp[i+2], cur);
                }
            }
        }

        return *max_element(dp.begin(), dp.end()) >= m;
    };

    int lo = 0, hi = MOD, mid = (lo + hi) / 2;
    while (lo < mid && mid < hi) {
        if (can(mid)) hi = mid;
        else lo = mid;
        mid = (lo + hi) / 2;
    }

    if (!can(hi)) {
        cout << -1 << '\n';
        return;
    }

    vector<char> ans(n, '?');
    int c = n;
    while (c > 0) {
        string p = build[c];
        if (sz(p) == 1) {
            ans[c-1] = p[0];
            c--;
        } else if (sz(p) == 2) {
            ans[c-1] = p[1];
            ans[c-2] = p[0];
            c -= 2;
        } else assert(false);
    }

    vector<int> ps(m + 1);
    for (int i = 0; i < n; i++) {
        int l = -1, r = -1;
        if (ans[i] == 'L') {
            l = a[i] - hi, r = a[i];
        } else if (ans[i] == 'R') {
            l = a[i], r = a[i] + hi;
        } else assert(false);

        int L = lower_bound(b.begin(), b.end(), l) - b.begin();
        int R = upper_bound(b.begin(), b.end(), r) - b.begin() - 1;
        if (L <= R) {
            ps[L]++;
            ps[R+1]--;
        }
    }

    for (int i = 1; i <= m; i++)
        ps[i] += ps[i-1];

    for (int i = 0; i < m; i++) {
        assert(ps[i]);
    }

    cout << hi << '\n';
    for (char c : ans) cout << c;
    cout << '\n';
}

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int T = 1;
    // cin >> T;
    while (T--) solve();
}

• Subtask 0: 0 / 0
• Subtask 1: 3 / 3
• Subtask 2: 6 / 6
• Subtask 3: 17 / 17
• Subtask 4: 0 / 27
• Subtask 5: 0 / 47