Submission #31624

#	Time	Username	Problem	Language	Result	Execution time	Memory
31624		minkank	Beads and wires (APIO14_beads)	C++14	100 / 100	854 ms	103244 KiB

beads

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

typedef pair<int, int> ii;

const int N = 2e5 + 5;

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

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

void redfs(int u, int p) {
    //if(u == 3) cout << g[p][0] << ' ' << g[p][1] << endl;
    if(a[p].size() == 1) g[p][1] = -1e9;
    sax[1][u][0] = -1e9;
    for(int i = 1; i <= cnt[u]; ++i) {
        int v = b[u][i].first, w = b[u][i].second;
        sax[0][u][i] = sax[0][u][i - 1] + max(dp[v][1] + w, dp[v][0]);
        sax[1][u][i] = sax[0][u][i - 1] + w + dp[v][0];
        sax[1][u][i] = max(sax[1][u][i], sax[1][u][i - 1] + max(dp[v][1] + w, dp[v][0]));
    }
    int W = 0;
    for(int i = 0; i < a[u].size(); ++i) if(a[u][i].first == p) W = a[u][i].second;
    if(u != 1) {
        cax[0][u][cnt[u] + 1] = max(g[p][1] + W, g[p][0]);
        cax[1][u][cnt[u] + 1] = W + g[p][0];
    }
    else cax[0][u][cnt[u] + 1] = 0, cax[1][u][cnt[u] + 1] = -1e9;
    for(int i = cnt[u]; i >= 1; --i) {
        int v = b[u][i].first, w = b[u][i].second;
        cax[0][u][i] = cax[0][u][i + 1] + max(dp[v][1] + w, dp[v][0]);
        cax[1][u][i] = cax[0][u][i + 1] + w + dp[v][0];
        cax[1][u][i] = max(cax[1][u][i], cax[1][u][i + 1] + max(dp[v][1] + w, dp[v][0]));
    }
    ans = max(ans, cax[0][u][1]);
    for(int i = 1; i <= cnt[u]; ++i) {
        int v = b[u][i].first;
        g[u][0] = sax[0][u][i - 1] + cax[0][u][i + 1];
        g[u][1] = max(sax[1][u][i - 1] + cax[0][u][i + 1], sax[0][u][i - 1] + cax[1][u][i + 1]);
        redfs(v, u);
    }
}

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() + 3, 0), r[i].assign(a[i].size() + 3, 0), b[i].assign(a[i].size() + 3, ii(0, 0)), sax[0][i].assign(a[i].size() + 3, 0), sax[1][i].assign(a[i].size() + 3, 0), cax[0][i].assign(a[i].size() + 3, 0), cax[1][i].assign(a[i].size() + 3, 0);
    dfs(1, 1);
    redfs(1, 1);
    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) {
                    ~~^~~~~~~~~~~~~
beads.cpp: In function 'void redfs(int, int)':
beads.cpp:50:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < a[u].size(); ++i) if(a[u][i].first == p) W = a[u][i].second;
                    ~~^~~~~~~~~~~~~

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