Submission #555521

#	Time	Username	Problem	Language	Result	Execution time	Memory
555521		alextodoran	Islands (IOI08_islands)	C++17	90 / 100	1383 ms	131072 KiB

islands

/**
 ____ ____ ____ ____ ____
||a |||t |||o |||d |||o ||
||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|

**/

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N_MAX = 1000000;

int N;
struct Edge {
    int to;
    int len;
};
vector <Edge> adj[N_MAX + 2];

bool seen[N_MAX + 2];
Edge par[N_MAX + 2];
int depth[N_MAX + 2];

tuple <int, int, int> backEdge;

int curr[N_MAX + 2];
void dfs (int u) {
    while (u != 0) {
        seen[u] = true;
        if (curr[u] < (int) adj[u].size()) {
            Edge e = adj[u][curr[u]++];
            if (seen[e.to] == false) {
                par[e.to] = Edge{u, e.len};
                depth[e.to] = depth[u] + 1;
                u = e.to;
            } else if (depth[e.to] > depth[u]) {
                backEdge = make_tuple(u, e.to, e.len);
            }
        } else {
            u = par[u].to;
        }
    }
}

bool root[N_MAX + 2];

ll maxAny[N_MAX + 2];
ll maxDown[N_MAX + 2];

void compute (int s) {
    queue <int> q; q.push(s);
    seen[s] = true; depth[s] = 0;
    vector <int> order;
    while (q.empty() == false) {
        int u = q.front(); q.pop();
        order.push_back(u);
        for (Edge e : adj[u]) {
            if (seen[e.to] == false && root[e.to] == false) {
                q.push(e.to);
                seen[e.to] = true;
                depth[e.to] = depth[u] + 1;
            }
        }
    }
    reverse(order.begin(), order.end());
    for (int u : order) {
        vector <ll> maxDowns;
        for (Edge e : adj[u]) {
            if (depth[u] < depth[e.to] && root[e.to] == false) {
                maxAny[u] = max(maxAny[u], maxAny[e.to]);
                maxDown[u] = max(maxDown[u], maxDown[e.to] + e.len);
                maxDowns.push_back(maxDown[e.to] + e.len);
            }
        }
        sort(maxDowns.begin(), maxDowns.end(), greater <ll> ());
        if ((int) maxDowns.size() >= 2) {
            maxAny[u] = max(maxAny[u], maxDowns[0] + maxDowns[1]);
        }
        maxAny[u] = max(maxAny[u], maxDown[u]);
    }
}

vector <vector <int>> rootGroups;

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> N;
    for (int u = 1; u <= N; u++) {
        Edge e;
        cin >> e.to >> e.len;
        adj[u].push_back(Edge{e.to, e.len});
        adj[e.to].push_back(Edge{u, e.len});
    }

    for (int u = 1; u <= N; u++) {
        if (seen[u] == false) {
            dfs(u);
            int v1, v2, len; tie(v1, v2, len) = backEdge;
            swap(v1, v2);
            par[v2] = Edge{v1, len};
            rootGroups.push_back({});
            int v = v1;
            while (v != v2) {
                root[v] = true;
                rootGroups.back().push_back(v);
                v = par[v].to;
            }
            root[v] = true;
            rootGroups.back().push_back(v);
        }
    }

    fill(seen + 1, seen + N + 1, false);
    for (int u = 1; u <= N; u++) {
        if (root[u] == true) {
            compute(u);
        }
    }

    ll answer = 0;
    for (vector <int> &roots : rootGroups) {
        ll totalLen = 0;
        ll maxLen = 0;
        for (int u : roots) {
            totalLen += par[u].len;
            maxLen = max(maxLen, maxAny[u]);
        }

        multiset <ll> s; ll len = 0;
        for (int i = (int) roots.size() - 1; i > 0; i--) {
            len += par[roots[i]].len;
            s.insert(maxDown[roots[i]] + len);
        }
        ll lazy = 0;

        for (int i = 0, u = roots[0]; i < (int) roots.size(); i++) {
            maxLen = max(maxLen, *s.rbegin() + lazy + maxDown[u]);
            s.insert(maxDown[u] - lazy);
            lazy += par[u].len;
            u = par[u].to;
            s.erase(s.find((maxDown[u] + totalLen) - lazy));
        }
        answer += maxLen;
    }
    cout << answer << "\n";

    return 0;
}

• 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: 10 / 10
• Subtask 9: 0 / 10