Submission #136121

#	Time	Username	Problem	Language	Result	Execution time	Memory
136121		fredbr	Beads and wires (APIO14_beads)	C++17	57 / 100	1062 ms	34696 KiB

beads

#include <bits/stdc++.h>

#pragma GCC optimize("O3")

using namespace std;
 
int const maxn = 202020;
int const inf = 0x3f3f3f3f;

struct Edge {
    int u, w, id;
};
 
struct FEdge {
    int a, b, w;
};

vector<Edge> v[maxn*3];
vector<FEdge> eg;

int dp[2*maxn][2];

inline int invalid(int x) {
    return v[x].size() == 1;
}
 
int solve(int id, int t = 0) {
    int x = eg[id].b;

    if (dp[id][t] != -1) return dp[id][t];

    int& d = dp[id][t];
    d = 0;
 
    if (t == 0) {
        for (Edge& e : v[x]) {
            if (id == (e.id^1)) continue;
            if (!invalid(e.u)) {
                d += max(solve(e.id, 1) + e.w, solve(e.id, 0));
            }
        }
    }
    else {
        int sum = solve(id, 0);
 
        for (Edge& e : v[x]) {
            if (id == (e.id^1)) continue;
 
            if (!invalid(e.u))
                d = max(d, sum - max(solve(e.id, 1) + e.w, solve(e.id, 0))
                           + e.w + solve(e.id, 0));
            else
                d = max(d, sum + e.w);
        }
    }
 
    return d;
}
 
int main() {
    memset(dp, -1, sizeof(dp));

    ios::sync_with_stdio(false), cin.tie(nullptr);
 
    int n;
    cin >> n;
 
    for (int i = 0; i < n-1; i++) {
        int a, b, w;
        cin >> a >> b >> w;
 
        v[a].push_back({b, w, i*2});
        v[b].push_back({a, w, i*2+1});

        eg.push_back({a, b, w});
        eg.push_back({b, a, w});
    }

    int ans = 0;
    for (int i = 1; i <= n; i++) {
        if (v[i].size() == 1) {
            v[n+1].push_back({i, -inf, 2*n-2});
            dp[2*n-2][0] = dp[2*n-2][1] = -1;
            eg.push_back({n+1, i, -inf});
            
            ans = max(ans, solve(2*n-2));

            eg.pop_back();
            dp[2*n-2][0] = dp[2*n-2][1] = -1;
            v[n+1].clear();
        }
    }

    cout << ans << "\n";
}

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 0 / 43