Submission #1037315

#	Time	Username	Problem	Language	Result	Execution time	Memory
1037315		yanb	Shortcut (IOI16_shortcut)	C++14	71 / 100	2071 ms	12892 KiB

shortcut

#include <bits/stdc++.h>
    
using namespace std;
    
#define int long long
#define pii pair<long long, long long>
    
int dfs(int n, vector<vector<pii>> &g, int v, int p) {
    int ans = 0;
    for (auto [u, du] : g[v]) {
        if (u != p) {
            ans = max(ans, dfs(u, g, u, v) + du);
        }
    }
    return ans;
}
    
int diam(int n, vector<signed> l, vector<signed> d) {
    vector<vector<pii>> g(2 * n);
    for (int i = 0; i < n - 1; i++) {
        g[i].push_back({i + 1, l[i]});
        g[i + 1].push_back({i, l[i]});
    }
    for (int i = 0; i < n; i++) {
        g[i].push_back({n + i, d[i]});
        g[n + i].push_back({i, d[i]});
    }
    
    int ans = 0;
    for (int i = 0; i < 2 * n; i++) ans = max(ans, dfs(n, g, i, i));
    return ans;
}
    
int find_shortcut(signed n, vector<signed> l, vector<signed> d, signed c) {
    int noshort = diam(n, l, d);

    vector<int> x(n);
    for (int i = 0; i < n - 1; i++) x[i + 1] = l[i] + x[i];
    
    int ll = 0, rr = 1e17;
    while (rr - ll > 1) {
        int mm = (ll + rr) / 2;
        int Xmn = -1e17, Ymn = -1e17, Xmx = 1e17, Ymx = 1e17; // X = y + z, Y = y - z  
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (x[j] - x[i] + (int) d[i] + (int) d[j] <= mm) continue;
                int goal = mm - c - (int) d[i] - (int) d[j];
                int zavg = x[j], ymin = x[i] - goal, ymax = x[i] + goal;
                Xmn = max(Xmn, ymin + zavg);
                Xmx = min(Xmx, ymax + zavg);
                Ymn = max(Ymn, ymin - zavg);
                Ymx = min(Ymx, ymax - zavg);
            }
        }
    
        bool ok = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                int X = x[i] + x[j], Y = x[i] - x[j];
                ok = ok || (Xmn <= X && X <= Xmx && Ymn <= Y && Y <= Ymx);
            }
        }
    
        if (ok) rr = mm;
        else ll = mm;
    }
    return min(rr, noshort);
}
    
#ifdef LOCAL
signed main() {
    int n, c;
    cin >> n >> c;
    vector<signed> l(n - 1), d(n);
    for (int i = 0; i < n - 1; i++) cin >> l[i];
    for (int i = 0; i < n; i++) cin >> d[i];
    cout << find_shortcut(n, l, d, c) << "\n";
}
#endif

Compilation message (stderr)

shortcut.cpp: In function 'long long int dfs(long long int, std::vector<std::vector<std::pair<long long int, long long int> > >&, long long int, long long int)':
shortcut.cpp:10:15: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   10 |     for (auto [u, du] : g[v]) {
      |               ^

• Subtask 1: 9 / 9
• Subtask 2: 14 / 14
• Subtask 3: 8 / 8
• Subtask 4: 7 / 7
• Subtask 5: 33 / 33
• Subtask 6: 0 / 22
• Subtask 7: 0 / 4
• Subtask 8: 0 / 3