Submission #1059289

#	Time	Username	Problem	Language	Result	Execution time	Memory
1059289		Zicrus	Islands (IOI08_islands)	C++17	16 / 100	419 ms	131072 KiB

islands

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

typedef long long ll;

ll n;
vector<vector<pair<ll, ll>>> adj; // length, node
vector<ll> rep;
vector<bool> vst;
vector<ll> comps;
vector<bool> cyc;
vector<pair<ll, ll>> nxt; // length, node
vector<ll> globToCyc;

ll cycRoot;
ll dfsCyc(ll cur, ll par) {
    vst[cur] = true;
    vector<pair<ll, ll>> numE;
    for (auto &e : adj[cur]) {
        if (e.second == par) continue;
        numE.push_back(e);
    }
    if (numE.size() == 2 && par == -1) {
        vst[numE[0].second] = true;
        cyc[cur] = cyc[numE[0].second] = true;
        cycRoot = cur;
        nxt[cur] = numE[0];
        nxt[numE[0].second] = {numE[1].first, cur};
        return -1;
    }
    for (auto &e : adj[cur]) {
        if (e.second == par) continue;
        if (vst[e.second] && !cyc[e.second]) {
            cyc[cur] = true;
            nxt[cur] = e;
            cycRoot = e.second;
            return e.second;
        }
        else {
            ll val = dfsCyc(e.second, cur);
            if (val == -1) continue;
            cyc[cur] = true;
            nxt[cur] = e;
            return cur == val ? -1 : val;
        }
    }
    return -1;
}

ll mxLen = 0;
ll dfsTreeSz(ll cur, ll par) {
    ll mx = 0;
    ll nxtMx = 0;
    for (auto &e : adj[cur]) {
        if (e.second == par) continue;
        if (cyc[e.second]) continue;
        ll val = e.first + dfsTreeSz(e.second, cur);
        if (val > mx) {
            nxtMx = mx;
            mx = val;
        }
        else if (val > nxtMx) {
            nxtMx = val;
        }
    }
    mxLen = max(mxLen, nxtMx + mx);
    return mx;
}

ll solveComp(ll root) {
    mxLen = 0;
    dfsCyc(root, -1);
    ll totLen = 0;
    ll x = cycRoot;
    vector<ll> cycle;
    do {
        globToCyc[x] = cycle.size();
        cycle.push_back(x);
        totLen += nxt[x].first;
        x = nxt[x].second;
    } while (x != cycRoot);
    vector<ll> treeSz(cycle.size());
    for (int i = 0; i < cycle.size(); i++) {
        treeSz[i] = dfsTreeSz(cycle[i], -1);
    }
    ll res = mxLen;
    ll mxId = cycle[0], mxVal = treeSz[0];
    ll lenSum = 0;
    ll cur = cycle[0];
    for (int i = 0; i < cycle.size(); i++) {
        if (cur == cycle[i] || mxId == cycle[i]) {
            lenSum = nxt[cur].first;
            cur = nxt[cur].second;
            mxId = globToCyc[cur];
            mxVal = lenSum + treeSz[globToCyc[cur]];
        }
        while (cur != cycle[i]) {
            ll val = lenSum + treeSz[globToCyc[cur]];
            if (val >= mxVal) {
                mxVal = val;
                mxId = globToCyc[cur];
            }
            lenSum += nxt[cur].first;
            cur = nxt[cur].second;
        }
        res = max(res, treeSz[i] + mxVal);
        lenSum -= nxt[cycle[i]].first;
        mxVal -= nxt[cycle[i]].first;
    }
    return res;
}

void dfs1(ll cur, ll rep1) {
    vst[cur] = true;
    rep[cur] = rep1;
    for (auto &e : adj[cur]) {
        if (vst[e.second]) continue;
        dfs1(e.second, rep1);
    }
}

int main() {
    cin >> n;
    adj = vector<vector<pair<ll, ll>>>(n);
    cyc = vector<bool>(n);
    nxt = vector<pair<ll, ll>>(n);
    globToCyc = vector<ll>(n);
    for (int i = 0; i < n; i++) {
        ll a, l;
        cin >> a >> l;
        adj[i].push_back({l, a-1});
        adj[a-1].push_back({l, i});
    }
    rep = vector<ll>(n);
    vst = vector<bool>(n);
    for (int i = 0; i < n; i++) {
        if (vst[i]) continue;
        dfs1(i, i);
        comps.push_back(i);
    }
    vst = vector<bool>(n);

    ll res = 0;
    for (auto &e : comps) {
        res += solveComp(e);
    }
    cout << res;
}

Compilation message (stderr)

islands.cpp: In function 'll solveComp(ll)':
islands.cpp:83:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |     for (int i = 0; i < cycle.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:90:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   90 |     for (int i = 0; i < cycle.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~

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