Submission #123451

#	Time	Username	Problem	Language	Result	Execution time	Memory
123451		popovicirobert	Beads and wires (APIO14_beads)	C++14	100 / 100	371 ms	30312 KiB

beads

#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long
// 217
// 44


/*const int MOD = ;

inline int lgput(int a, int b) {
    int ans = 1;
    while(b > 0) {
        if(b & 1) ans = (1LL * ans * a) % MOD;
        b >>= 1;
        a = (1LL * a * a) % MOD;
    }
    return ans;
}

inline void mod(int &x) {
    if(x >= MOD)
        x -= MOD;
}

inline void add(int &x, int y) {
    x += y;
    mod(x);
}

inline void sub(int &x, int y) {
    x += MOD - y;
    mod(x);
}


inline void mul(int &x, int y) {
    x = (1LL * x * y) % MOD;
}*/


using namespace std;

const ll INF = 1e15;
const int MAXN = (int) 2e5;

vector < pair <int, int> > g[MAXN + 1];
ll dp[MAXN + 1][2], cst[MAXN + 1];
// dp[nod][0] = nu ai spart nimic
// dp[nod][1] = ai spart un fiu de tata

void dfs(int nod, int par) {
    vector <ll> cur(2, -INF);
    cur[0] = 0;

    for(auto it : g[nod]) {
        if(it.first != par) {
            cst[it.first] = it.second;
            dfs(it.first, nod);

            ll mx = max(dp[it.first][1] + it.second, dp[it.first][0]);
            cur[1] = max(cur[0] + dp[it.first][0] + it.second, cur[1] + mx);
            cur[0] += mx;
        }
    }
    dp[nod][0] = cur[0], dp[nod][1] = cur[1];
}

ll ans;

void solve(int nod, int par) {
    ans = max(ans, dp[nod][0]);

    vector < pair <ll, int> > vals;
    for(auto it : g[nod]) {
        vals.push_back({dp[it.first][0] + it.second - max(dp[it.first][0], dp[it.first][1] + it.second), it.first});
    }
    sort(vals.begin(), vals.end(), greater < pair <ll, int> >());

    for(auto it : g[nod]) {
        if(it.first != par) {
            ll a = dp[nod][0], b = dp[nod][1], c = dp[it.first][0], d = dp[it.first][1];
            ll mx = max(dp[it.first][0], dp[it.first][1] + it.second);

            dp[nod][0] -= mx;
            if(it.first != vals[0].second) {
                dp[nod][1] -= mx;
            }
            else {
                if(vals.size() > 1) {
                    dp[nod][1] -= dp[it.first][0] + it.second;
                    dp[nod][1] += vals[1].first;
                }
                else {
                    dp[nod][1] = -INF;
                }
            }

            mx = max(dp[nod][0], dp[nod][1] + it.second);
            dp[it.first][1] = max(dp[it.first][1] + mx, dp[it.first][0] + dp[nod][0] + it.second);
            dp[it.first][0] += mx;

            solve(it.first, nod);

            dp[nod][0] = a, dp[nod][1] = b, dp[it.first][0] = c, dp[it.first][1] = d;
        }
    }
}

int main() {
    //ifstream cin("A.in");
    //ofstream cout("A.out");
    int i, n;
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    cin >> n;

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

    dfs(1, 0);
    solve(1, 0);

    cout << ans;

    //cin.close();
    //cout.close();
    return 0;
}

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