Submission #31655

#	Time	Username	Problem	Language	Result	Execution time	Memory
31655		minhtung0404	Beads and wires (APIO14_beads)	C++14	100 / 100	453 ms	23028 KiB

beads

#include<bits/stdc++.h>
const int N = 2e5 + 5;
const int inf = 1e9;
using namespace std;

typedef pair <int, int> ii;
vector <ii> adj[N];
int n, f[N][2], g[N][2], p[N], a, b, c, maxxx, co[N], ans[N];
int maxx[N][2], L[N][2], R[N][2];

void dfs(int u){
    int ma = -inf;
    f[u][1] = -inf;
    f[u][0] = 0;
    for(int i = 0; i < adj[u].size(); i++){
        int v = adj[u][i].first;
        if (v == p[u]) continue;
        p[v] = u;
        dfs(v);
    }
    for (int i = 0; i < adj[u].size(); i++){
        int v = adj[u][i].first, cost = adj[u][i].second;
        if (v == p[u]) continue;
        f[u][0] += max(f[v][1]+cost, f[v][0]);
        co[v] = cost;
        if (f[v][1]+cost > f[v][0]) ma = max(ma, f[v][0] - f[v][1]);
        else ma = max(ma, cost);
    }
    f[u][1] = f[u][0] + ma;
}

void DFS(int u){
    int cak = co[u], sz = adj[u].size();
    if (g[u][1] + co[u] > g[u][0]) cak = g[u][0] - g[u][1];
    ans[u] = g[u][0] + f[u][0];

    L[0][0] = 0;
    L[0][1] = -inf;
    maxx[0][0] = -inf;
    for (int i = 0; i < sz; i++){
        int v = adj[u][i].first, cost = adj[u][i].second;
        if (v == p[u]) {
            L[i+1][0] = L[i][0];
            L[i+1][1] = L[i][1];
            maxx[i+1][0] = maxx[i][0];
            continue;
        }
        L[i+1][0] = L[i][0] + max(f[v][0], f[v][1] + cost);

        int z;
        if (f[v][0] > f[v][1] + cost) z = cost;
        else z = f[v][0] - f[v][1];

        maxx[i+1][0] = max(maxx[i][0], z);
        L[i+1][1] = L[i+1][0] + maxx[i+1][0];
    }
    R[sz+1][0] = 0;
    R[sz+1][1] = -inf;
    maxx[sz+1][1] = -inf;
    for (int i = sz-1; i >= 0; i--){
        int v = adj[u][i].first, cost = adj[u][i].second;
        if (v == p[u]) {
            R[i+1][0] = R[i+2][0];
            R[i+1][1] = R[i+2][1];
            maxx[i+1][1] = maxx[i+2][1];
            continue;
        }
        R[i+1][0] = R[i+2][0] + max(f[v][0], f[v][1] + cost);
        int z;
        if (f[v][0] > f[v][1] + cost) z = cost;
        else z = f[v][0] - f[v][1];
        maxx[i+1][1] = max(maxx[i+2][1], z);
        R[i+1][1] = R[i+1][0] + maxx[i+1][1];
    }
    for (int i = 0; i < sz; i++){
        int v = adj[u][i].first, cost = adj[u][i].second;
        if (v == p[u]) continue;
        g[v][0] = max(g[v][0], g[u][0] + L[i][0] + R[i+2][0]);
        g[v][0] = max(g[v][0], g[u][1] + L[i][0] + R[i+2][0] + cost);
        g[v][0] = max(g[v][0], g[u][0] + L[i][1] + R[i+2][0] + cost);
        g[v][0] = max(g[v][0], g[u][0] + L[i][0] + R[i+2][1] + cost);
        g[v][1] = g[u][0] + L[i][0] + R[i+2][0] + cost;
    }

    for (int i = 0; i < sz; i++){
        int v = adj[u][i].first;
        if (v == p[u]) continue;
        DFS(v);
    }
}

int main(){
    cin >> n;
    for (int i = 1; i < n; i++){
        cin >> a >> b >> c;
        adj[a].push_back(ii(b, c));
        adj[b].push_back(ii(a, c));
    }
    dfs(1);
    g[1][1] = -inf;
    DFS(1);
    for (int i = 1; i <= n; i++){
        maxxx = max(maxxx, ans[i]);
    }
    cout << maxxx;
}
/*
5
1 2 10
1 3 40
1 4 15
1 5 20

10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34
*/

Compilation message (stderr)

beads.cpp: In function 'void dfs(int)':
beads.cpp:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < adj[u].size(); i++){
                    ~~^~~~~~~~~~~~~~~
beads.cpp:21:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < adj[u].size(); i++){
                     ~~^~~~~~~~~~~~~~~
beads.cpp: In function 'void DFS(int)':
beads.cpp:33:9: warning: variable 'cak' set but not used [-Wunused-but-set-variable]
     int cak = co[u], sz = adj[u].size();
         ^~~

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