Submission #219648

#	Time	Username	Problem	Language	Result	Execution time	Memory
219648		tatyam	Islands (IOI08_islands)	C++17	80 / 100	2075 ms	131076 KiB

islands

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
template<class T> using pq = priority_queue<T, vector<T>, greater<T>>;
const ll INF = 0x1fffffffffffffff;
#define overload3(a,b,c,d,...) d
#define all(a) begin(a), end(a)
#define rep1(n) for(int i = 0; i < n; i++)
#define rep2(i,n) for(int i = 0; i < n; i++)
#define rep3(i,a,b) for(int i = a; i < b; i++)
#define rep(...) overload3(__VA_ARGS__, rep3, rep2, rep1)(__VA_ARGS__)
#define each(i,a) for(auto&& i : a)
 
template<class T, class U> bool chmin(T& a, const U& b){ if(a > b){ a = b; return 1; } return 0; }
template<class T, class U> bool chmax(T& a, const U& b){ if(a < b){ a = b; return 1; } return 0; }
 
 
 
struct SlidMax{
    deque<pair<ll, int>> q; // 8MB?
    int low = 0, high = 0;
    ll pop(){
        ll ans = q[0].first;
        if(q.front().second == low++) q.pop_front();
        return ans;
    }
    void push(ll x){
        while(q.size() && q.back().first <= x) q.pop_back();
        q.emplace_back(x, high++);
    }
};
ll Diameter(const vector<vector<pii>>& g){
    int n = g.size();
    vector<ll> cost(n, INF); // 8MB
    vector<bool> used(n); // 1MB
    pq<pii> q; // 8MB
    q.emplace(0, 0);
    cost[0] = 0;
    while(q.size()){
        int at = q.top().second;
        q.pop();
        if(used[at]) continue;
        used[at] = 1;
        each(i, g[at]) if(chmin(cost[i.first], cost[at] + i.second)) q.emplace(cost[i.first], i.first);
    }
    int d = max_element(all(cost)) - cost.begin();
    cost.assign(n, INF);
    used.assign(n, 0);
    q.emplace(0, d);
    cost[d] = 0;
    while(q.size()){
        int at = q.top().second;
        q.pop();
        if(used[at]) continue;
        used[at] = 1;
        each(i, g[at]) if(chmin(cost[i.first], cost[at] + i.second)) q.emplace(cost[i.first], i.first);
    }
    return *max_element(all(cost));
}
ll solve(const vector<vector<pii>>& g){
    int n = g.size();
    int at = 0;
    vector<bool> circle(n); // 1MB
    rep(n) at = g[at][0].first;
    rep(n){
        at = g[at][0].first;
        circle[at] = 1;
    }
    vector<ll> d(n); // 8MB
    auto dfs = [&](int from, int at, const auto& f) -> void {
        rep(i, 1, g[at].size()){
            const int to = g[at][i].first;
            if(to != from && !circle[to]){
                f(at, to, f);
                chmax(d[at], d[to] + g[at][i].second);
            }
        }
    };
    rep(n) if(circle[i]) dfs(-1, i, dfs); // 20MB
    ll ans = Diameter(g);
    int circle_size = accumulate(all(circle), 0);
    vector<ll> len(circle_size * 2 + 1); // 16MB
    rep(circle_size * 2){
        int to = g[at][0].first;
        len[i + 1] = len[i] + g[at][0].second;
        at = to;
    }
    SlidMax mx;
    rep(circle_size - 1){
        at = g[at][0].first;
        mx.push(len[i + 1] + d[at]);
    }
    at = g[at][0].first;
    rep(circle_size){
        chmax(ans, mx.pop() - len[i] + d[at]);
        mx.push(len[circle_size + i] + d[at]);
        at = g[at][0].first;
    }
    return ans;
}
int main(){
    int n;
    cin >> n;
    vector<vector<pii>> G(n); // 24MB
    rep(n){
        int a, b;
        cin >> a >> b;
        a--;
        G[i].emplace_back(a, b);
    }
    rep(n) G[G[i][0].first].emplace_back(i, G[i][0].second);
    vector<int> idx(n, -1); // 4MB
    ll ans = 0;
    rep(n) if(idx[i] == -1){
        vector<int> vertex = {i};
        idx[i] = 0;
        for(int i = 0; i < vertex.size(); i++){
            for(auto& [to, d] : G[vertex[i]]){
                if(idx[to] == -1){
                    idx[to] = vertex.size();
                    vertex.push_back(to);
                }
            }
        }
        int n = vertex.size();
        vector<vector<pii>> g(n);
        rep(n){
            auto& edge = G[vertex[i]][0];
            g[i].emplace_back(idx[edge.first], edge.second);
        }
        each(i, vertex){
            G[i].clear();
            G[i].shrink_to_fit();
        }
        vertex.clear();
        vertex.shrink_to_fit();
        rep(n){
            auto& edge = g[i][0];
            g[edge.first].emplace_back(i, edge.second);
        }
        ans += solve(g);
    }
    cout << ans << endl;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:118:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0; i < vertex.size(); i++){
                        ~~^~~~~~~~~~~~~~~
islands.cpp:119:29: warning: unused variable 'd' [-Wunused-variable]
             for(auto& [to, d] : G[vertex[i]]){
                             ^
islands.cpp: In instantiation of 'solve(const std::vector<std::vector<std::pair<int, int> > >&)::<lambda(int, int, const auto:1&)> [with auto:1 = solve(const std::vector<std::vector<std::pair<int, int> > >&)::<lambda(int, int, const auto:1&)>]':
islands.cpp:80:40:   required from here
islands.cpp:11:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 #define rep3(i,a,b) for(int i = a; i < b; i++)
                                      ^
islands.cpp:7:32: note: in expansion of macro 'rep3'
 #define overload3(a,b,c,d,...) d
                                ^
islands.cpp:12:18: note: in expansion of macro 'overload3'
 #define rep(...) overload3(__VA_ARGS__, rep3, rep2, rep1)(__VA_ARGS__)
                  ^~~~~~~~~
islands.cpp:72:9: note: in expansion of macro 'rep'
         rep(i, 1, g[at].size()){
         ^~~

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10