Submission #166535

#	Time	Username	Problem	Language	Result	Execution time	Memory
166535		combi1k1	Beads and wires (APIO14_beads)	C++14	100 / 100	242 ms	25156 KiB

beads

#include<bits/stdc++.h>

using namespace std;

#define pb  emplace_back

#define int long long

const int   N   = 2e5 + 1;

typedef pair<int,int>   ii;

vector<ii>  g[N];

int f[N][2];
int ans = 0;

void dfs(int u,int p)   {
    int mx = -1e9;
    for(ii  e : g[u])   {
        int v = e.first;
        int c = e.second;
        if (v == p) continue;
        dfs(v,u);

        f[u][0] += max(f[v][1] + c,f[v][0]);

        if (mx < min(c,f[v][0] - f[v][1]))
            mx = min(c,f[v][0] - f[v][1]);
    }
    f[u][1] = f[u][0] + mx;
}
void cal(int u,int p,int lz)    {
    ans = max(ans,f[u][0]);

    int Sum = f[u][0];
    int mx1 = lz;
    int mx2 = -1e9;

    for(ii  e : g[u])   {
        int v = e.first;
        int c = e.second;
        if (v ^ p)  {
            if (mx2 < min(c,f[v][0] - f[v][1]))
                mx2 = min(c,f[v][0] - f[v][1]);
            if (mx1 < mx2)
                swap(mx1,mx2);
        }
    }
    for(ii  e : g[u])   {
        int v = e.first;
        int c = e.second;
        if (v ^ p)  {
            int prv = max(f[v][1] + c,f[v][0]);
            int cur = min(c,f[v][0] - f[v][1]);

            if (cur ^ mx1)
                cur = mx2;

            cur = mx1 + mx2 - cur;

            Sum -= prv; //now Sum is equal to f[u][0] when we start dfs from node v

            f[v][0] += max(cur + c,0ll) + Sum;
            f[v][1]  = max(cur + f[v][0],f[v][1]);

            cal(v,u,min(c,-cur));
            Sum += prv;
        }
    }
}

signed main()   {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    int n;  cin >> n;

    for(int i = 1 ; i < n ; ++i)    {
        int x;  cin >> x;
        int y;  cin >> y;
        int c;  cin >> c;
        g[x].pb(y,c);
        g[y].pb(x,c);
    }

    dfs(1,0);
    cal(1,0,-1e9);

    cout << ans << endl;
}
/*
5
1 2 10
1 3 40
1 4 15
1 5 20
*/

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