Submission #494909

#	Time	Username	Problem	Language	Result	Execution time	Memory
494909		Stickfish	Beads and wires (APIO14_beads)	C++17	100 / 100	188 ms	22188 KiB

beads

#include <iostream>
#include <vector>
using namespace std;

const int MAXN = 2e5 + 123;
const int INF = 1.77013e9;
vector<pair<int, int>> edg[MAXN];
int dp0[MAXN];
int dp1[MAXN];

void update(int v, int rt) {
    dp0[v] = dp1[v] = 0;
    int rtw = -INF;
    for (auto [u, w] : edg[v]) {
        if (u == rt) {
            rtw = w;
            continue;
        }
        dp0[v] += max(dp0[u], dp1[u]);
    }
    dp1[v] = dp0[v];
    if (rtw != -INF) {
        for (auto [u, w] : edg[v]) {
            if (u == rt)
                continue;
            dp1[v] = max(dp1[v], dp0[v] + rtw + w + min(0, dp0[u] - dp1[u]));
        }
    }
}

void get_ans(int v, int rt) {
    for (auto [u, w] : edg[v]) {
        if (u == rt) {
            continue;
        }
        get_ans(u, v);
    }
    update(v, rt);
}

int dfs(int v, int rt) {
    int dpv0 = dp0[v];
    int dpv1 = dp1[v];
    int ans = dp0[v];
    int a0 = -INF;
    int a1 = -INF;
    for (auto [u, w] : edg[v]) {
        int x = w + min(0, dp0[u] - dp1[u]);
        if (x > a0) {
            a1 = a0;
            a0 = x;
        } else if (x > a1) {
            a1 = x;
        }
    }
    
    for (auto [u, w] : edg[v]) {
        if (u == rt)
            continue;
        int dpu0 = dp0[u];
        int dpu1 = dp1[u];
        dp0[v] -= max(dp0[u], dp1[u]);
        dp1[v] = dp0[v];
        int x = w + min(0, dp0[u] - dp1[u]);
        if (x == a0) {
            if (a1 != -INF)
                dp1[v] = max(dp1[v], dp0[v] + w + a1);
        } else if (a0 != -INF) {
            dp1[v] = max(dp1[v], dp0[v] + w + a0);
        }
        
        update(u, -1);
        ans = max(ans, dfs(u, v));
        dp0[v] = dpv0;
        dp1[v] = dpv1;
        dp0[u] = dpu0;
        dp1[u] = dpu1;
    }
    return ans;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n;
    cin >> n;
    for (int i = 0; i < n - 1; ++i) {
        int u, v, d;
        cin >> u >> v >> d;
        --u, --v;
        edg[u].push_back({v, d});
        edg[v].push_back({u, d});
    }
    get_ans(0, -1);
    int ans = dfs(0, -1);
    cout << ans << '\n';
}

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