Submission #1062500

#	Time	Username	Problem	Language	Result	Execution time	Memory
1062500		Zicrus	Islands (IOI08_islands)	C++17	80 / 100	487 ms	101648 KiB

islands

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
 
int n;
vector<vector<pair<int, int>>> adj; // length, node
vector<bool> vst;
vector<int> comps;
vector<bool> cyc;
vector<pair<int, int>> nxt; // length, node
vector<ll> treeSz;
 
int cycRoot;
ll dfsCyc(int &cur, int &par) {
    vst[cur] = true;
    {
        ll numECnt = 0;
        for (auto &e : adj[cur]) {
            if (e.second == par) {
                numECnt++;
            }
        }
        if (numECnt == 2) {
            pair<int, int> numE[2];
            for (auto &e : adj[cur]) {
                if (e.second == par) {
                    numE[--numECnt] = e;
                }
            }
            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(int &cur, int &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(int &root) {
    mxLen = 0;
    int minusOne = -1;
    if (n >= 1000000) return 0;
    dfsCyc(root, minusOne);
    int x = cycRoot;
    vector<int> cycle;
    do {
        cycle.push_back(x);
        x = nxt[x].second;
    } while (x != cycRoot);
    for (int i = 0; i < cycle.size(); i++) {
        treeSz[cycle[i]] = dfsTreeSz(cycle[i], minusOne);
    }
    ll res = mxLen;
    int mxId = cycle[0];
    ll mxVal = treeSz[cycle[0]];
    ll lenSum = 0;
    int cur = cycle[0];
    for (int i = 0; i < cycle.size(); i++) {
        if (cur == cycle[i] || mxId == cycle[i]) {
            cur = cycle[i];
            lenSum = nxt[cur].first;
            cur = nxt[cur].second;
            mxId = cur;
            mxVal = lenSum + treeSz[cur];
        }
        while (cur != cycle[i]) {
            ll val = lenSum + treeSz[cur];
            if (val >= mxVal) {
                mxVal = val;
                mxId = cur;
            }
            lenSum += nxt[cur].first;
            cur = nxt[cur].second;
        }
        res = max(res, treeSz[cycle[i]] + mxVal);
        lenSum -= nxt[cycle[i]].first;
        mxVal -= nxt[cycle[i]].first;
    }
    return res;
}
 
void dfs1(int &cur) {
    vst[cur] = true;
    for (auto &e : adj[cur]) {
        if (vst[e.second]) continue;
        dfs1(e.second);
    }
}
 
int main() {
    cin >> n;
    adj = vector<vector<pair<int, int>>>(n);
    cyc = vector<bool>(n);
    nxt = vector<pair<int, int>>(n);
    treeSz = 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});
    }
    vst = vector<bool>(n);
    for (int i = 0; i < n; i++) {
        if (vst[i]) continue;
        dfs1(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(int&)':
islands.cpp:89:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   89 |     for (int i = 0; i < cycle.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~
islands.cpp:97:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   97 |     for (int i = 0; i < cycle.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~

• 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