Submission #145290

#	Time	Username	Problem	Language	Result	Execution time	Memory
145290		dolphingarlic	Beads and wires (APIO14_beads)	C++14	100 / 100	467 ms	32868 KiB

beads

#include <bits/stdc++.h>
#pragma GCC Optimize("O3")
#define FOR(i, x, y) for (int i = x; i < y; i++)
#define MOD 1000000007
typedef long long ll;
using namespace std;

#define N 234567
#define mp make_pair
#define pb push_back
#define INF 1000000000000LL

int n, a, b;
ll w, pw[N], dp[N][2][2];
vector<pair<int, ll> > al[N];
void dfs(int node, int par) {
    if (al[node].size() == 1 && par != -1) return;
    ll sc = 0, bst_mid = -INF, bst_unuse_mid = -INF, bst_unuse_mid2 = -INF,
       bst_unuse_nomid = -INF, bst_unuse_nomid2 = -INF;
    int bst_unuse_mid_child, bst_unuse_mid_child2, bst_unuse_nomid_child,
        bst_unuse_nomid_child2;
    for (int i = 0; i < al[node].size(); i++)
        if (al[node][i].first != par) {
            int child = al[node][i].first;
            ll edge = al[node][i].second;
            pw[child] = edge;
            dfs(child, node);
            ll normsc = max(dp[child][0][0], dp[child][1][0]);
            sc += normsc;
            ll midsc = max(dp[child][0][1], dp[child][1][1]) - normsc;
            if (midsc > bst_mid) bst_mid = midsc;
            ll unuse_midsc = dp[child][0][1] + edge - normsc;
            if (unuse_midsc > bst_unuse_mid) {
                bst_unuse_mid2 = bst_unuse_mid;
                bst_unuse_mid_child2 = bst_unuse_mid_child;
                bst_unuse_mid = unuse_midsc;
                bst_unuse_mid_child = child;
            } else if (unuse_midsc > bst_unuse_mid2) {
                bst_unuse_mid2 = unuse_midsc;
                bst_unuse_mid_child2 = child;
            }
            ll unuse_nomidsc = dp[child][0][0] + edge - normsc;
            if (unuse_nomidsc > bst_unuse_nomid) {
                bst_unuse_nomid2 = bst_unuse_nomid;
                bst_unuse_nomid_child2 = bst_unuse_nomid_child;
                bst_unuse_nomid = unuse_nomidsc;
                bst_unuse_nomid_child = child;
            } else if (unuse_nomidsc > bst_unuse_nomid2) {
                bst_unuse_nomid2 = unuse_nomidsc;
                bst_unuse_nomid_child2 = child;
            }
        }
    dp[node][0][0] = sc;
    dp[node][0][1] = sc + max(0LL, bst_mid);
    dp[node][0][1] =
        max(dp[node][0][1], sc + bst_unuse_nomid + bst_unuse_nomid2);
    if (bst_unuse_mid_child != bst_unuse_nomid_child)
        dp[node][0][1] =
            max(dp[node][0][1], sc + bst_unuse_nomid + bst_unuse_mid);
    else {
        dp[node][0][1] =
            max(dp[node][0][1], sc + bst_unuse_nomid2 + bst_unuse_mid);
        dp[node][0][1] =
            max(dp[node][0][1], sc + bst_unuse_nomid + bst_unuse_mid2);
    }

    dp[node][1][0] = sc + pw[node] + bst_unuse_nomid;
    dp[node][1][1] = sc + pw[node] + bst_unuse_mid;
}

int main() {
    cin >> n;
    for (int i = 0; i < n - 1; i++) {
        cin >> a >> b >> w;
        al[a].pb(mp(b, w));
        al[b].pb(mp(a, w));
    }
    dfs(1, -1);

    cout << max(dp[1][0][1], dp[1][0][0]) << '\n';
    return 0;
}

Compilation message (stderr)

beads.cpp:2:0: warning: ignoring #pragma GCC Optimize [-Wunknown-pragmas]
 #pragma GCC Optimize("O3")
 
beads.cpp: In function 'void dfs(int, int)':
beads.cpp:22:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < al[node].size(); i++)
                     ~~^~~~~~~~~~~~~~~~~
beads.cpp:20:30: warning: variable 'bst_unuse_mid_child2' set but not used [-Wunused-but-set-variable]
     int bst_unuse_mid_child, bst_unuse_mid_child2, bst_unuse_nomid_child,
                              ^~~~~~~~~~~~~~~~~~~~
beads.cpp:21:9: warning: variable 'bst_unuse_nomid_child2' set but not used [-Wunused-but-set-variable]
         bst_unuse_nomid_child2;
         ^~~~~~~~~~~~~~~~~~~~~~
beads.cpp:57:5: warning: 'bst_unuse_nomid_child' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if (bst_unuse_mid_child != bst_unuse_nomid_child)
     ^~
beads.cpp:57:5: warning: 'bst_unuse_mid_child' may be used uninitialized in this function [-Wmaybe-uninitialized]

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