Submission #944089

#	Time	Username	Problem	Language	Result	Execution time	Memory
944089		wii	Dreaming (IOI13_dreaming)	C++17	100 / 100	81 ms	32284 KiB

dreaming

#include "dreaming.h"
#include <bits/stdc++.h>
using namespace std;
 
#define sz(x) (int)(x).size()
const int MaxN = 1e5 + 5;
 
template<typename T> bool maximize(T &res, const T &val) { if (res < val) { res = val; return true; } return false; }
template<typename T> bool minimize(T &res, const T &val) { if (val < res) { res = val; return true; } return false; }
 
const int Inf = 0x3f3f3f3f;
 
int n, m, l;
vector<int> pref[MaxN], suff[MaxN];
vector<pair<int, int>> adj[MaxN];
 
int vis[MaxN];
int dep[MaxN], dp[MaxN];
void dfs(int u, int p) {
    vis[u] = true;
 
    for (auto [v, w]: adj[u]) if (v != p) {
        dep[v] = dep[u] + w;
        dfs(v, u);
 
        maximize(dp[u], dp[v] + w);
    }
}
 
int ans, diameter;
void reroot(int u, int p) {
    minimize(ans, dp[u]);
    maximize(diameter, dp[u]);
 
    for (int i = 0; i < sz(adj[u]); ++i) {
        auto [v, w] = adj[u][i];
        pref[u].emplace_back(dp[v] + w);
        suff[u].emplace_back(dp[v] + w);
    }
 
    for (int i = 0; i < sz(adj[u]); ++i) {
        auto [v, w] = adj[u][i];
        if (i) maximize(pref[u][i], pref[u][i - 1]);
    }
 
    for (int i = sz(adj[u]) - 1; i >= 0; --i) {
        auto [v, w] = adj[u][i];
        if (i + 1 < sz(adj[u])) maximize(suff[u][i], suff[u][i + 1]);
    }
 
    for (int i = 0; i < sz(adj[u]); ++i) {
        auto [v, w] = adj[u][i];
        if (v == p) continue;
 
        int old = dp[v];
        int nw = max((i ? pref[u][i - 1] : 0), (i + 1 < sz(adj[u]) ? suff[u][i + 1] : 0));
 
        dp[u] = nw;
        dp[v] = max(dp[u] + w, old);
 
        reroot(v, u);
 
        dp[u] = pref[u].back();
        dp[v] = old;
    }
}
 
int used[MaxN];
int travelTime(int N, int M, int L, int A[], int B[], int T[]) {
    n = N;
    m = M;
    l = L;
 
    for (int i = 0; i < m; ++i) {
        int u = A[i];
        int v = B[i];
        int w = T[i];
 
        adj[u].emplace_back(v, w);
        adj[v].emplace_back(u, w);
    }
 
    vector<int> best;
 
    if (1)
    for (int i = 0; i < n; ++i) if (!vis[i]) {
        dfs(i, i);
 
        ans = Inf;
        reroot(i, i);
 
        best.push_back(ans);
    }
 
    sort(best.begin(), best.end(), greater<int>());
    int maxD = 0;
 
    maximize(maxD, best[0]);
    if (best.size() >= 2) maximize(maxD, best[0] + best[1] + l);
    if (best.size() >= 3) maximize(maxD, best[1] + best[2] + 2*l);
 
    return max(maxD, diameter);
}

Compilation message (stderr)

dreaming.cpp: In function 'void reroot(int, int)':
dreaming.cpp:42:14: warning: structured binding declaration set but not used [-Wunused-but-set-variable]
   42 |         auto [v, w] = adj[u][i];
      |              ^~~~~~
dreaming.cpp:47:14: warning: structured binding declaration set but not used [-Wunused-but-set-variable]
   47 |         auto [v, w] = adj[u][i];
      |              ^~~~~~

• Subtask 1: 14 / 14
• Subtask 2: 10 / 10
• Subtask 3: 23 / 23
• Subtask 4: 18 / 18
• Subtask 5: 12 / 12
• Subtask 6: 23 / 23