Submission #31607

#	Time	Username	Problem	Language	Result	Execution time	Memory
31607		minkank	Beads and wires (APIO14_beads)	C++14	0 / 100	9 ms	2432 KiB

beads

#include <bits/stdc++.h>
using namespace std;

typedef pair<int, int> ii;

const int N = 1e4 + 5;

int n, dp[N][2], ans;
vector<ii> a[N], b[N];
vector<int> l[N], r[N];

void dfs(int u, int p) {
    dp[u][0] = dp[u][1] = 0;
    int cnt = 0;
    for(int i = 0; i < a[u].size(); ++i) {
        int v = a[u][i].first;
        if(v == p) continue;
        dfs(v, u);
        cnt++; b[u][cnt] = a[u][i];
    }
    l[u][0] = 0;
    for(int i = 1; i <= cnt; ++i) {
        int v = b[u][i].first, w = b[u][i].second;
        l[u][i] = l[u][i - 1] + max(dp[v][1] + w, dp[v][0]);
    }
    r[u][cnt + 1] = 0;
    for(int i = cnt; i >= 1; --i) {
        int v = b[u][i].first, w = b[u][i].second;
        r[u][i] = r[u][i + 1] + max(dp[v][1] + w, dp[v][0]);
    }
    dp[u][0] = l[u][cnt];
    for(int i = 1; i <= cnt; ++i) {
        int v = b[u][i].first, w = b[u][i].second;
        dp[u][1] = max(dp[u][1], l[u][i - 1] + r[u][i + 1] + dp[v][0] + w);
    }
    if(a[u].size() == 1) dp[u][1] = -1e9;
}

int main() {
    cin >> n;
    for(int i = 1; i < n; ++i) {
        int u, v, w;
        cin >> u >> v >> w;
        a[u].push_back(ii(v, w));
        a[v].push_back(ii(u, w));
    }
    for(int i = 1; i <= n; ++i) l[i].assign(a[i].size() + 2, 0), r[i].assign(a[i].size() + 2, 0), b[i].assign(a[i].size() + 2, ii(0, 0));
    vector<int> pos; for(int i = 1; i <= n; ++i) pos.push_back(i);
    random_shuffle(pos.begin(), pos.end());
    for(int p = 0; p <= 100; ++p) {
        int i = pos[p];
        dfs(i, i);
        ans = max(ans, dp[i][0]);
    }
    cout << ans;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs(int, int)':
beads.cpp:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < a[u].size(); ++i) {
                    ~~^~~~~~~~~~~~~

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