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Submission #998702

# Submission time Handle Problem Language Result Execution time Memory
998702 2024-06-14T14:26:05 Z Ghetto Islands (IOI08_islands) C++17
90 / 100
 1191 ms 131072 KB 
#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pii = pair<int, int>;
using pil = pair<int, lint>;
using pli = pair<lint, int>;
const int MAX_N = 1e6 + 5;
 
int n;
int to[MAX_N];
vector<pil> from[MAX_N];
 
bool seen[MAX_N];
void dfs1(int s) {
    stack<int> ord; ord.push(s);
    while (ord.size()) {
        int u = ord.top(); ord.pop();
        seen[u] = true;
        if (!seen[to[u]]) ord.push(to[u]);
        for (pil x : from[u])
            if (!seen[x.first]) ord.push(x.first);
    }
}
 
vector<int> cyc; // Reverse order btw
bool in_cyc[MAX_N];
bool vis[MAX_N];
void dfs2(int s) {
    vector<int> bef;
    stack<int> ord; ord.push(s);
    while (ord.size()) {
        int u = ord.top(); ord.pop();
        vis[u] = true, bef.push_back(u);
        int v = to[u];
        if (!vis[v]) { ord.push(v); continue; }
        int i = bef.size() - 1;
        while (true) {
            cyc.push_back(bef[i]), in_cyc[bef[i]] = true;
            if (bef[i] == v) break;
            i--;
        }
        break;
    }
}
 
lint dp[MAX_N];
lint best[MAX_N];
int par[MAX_N];
lint dfs3(int s) {
    vector<int> preord;
    stack<int> ord; ord.push(s);
    while (ord.size()) {
        int u = ord.top(); ord.pop();
        preord.push_back(u);
        for (pil x : from[u]) {
            int v = x.first;
            if (v == par[u] || in_cyc[v]) continue;
            par[v] = u, ord.push(v);
        }
    }

    for (int i = preord.size() - 1; i >= 0; i--) {
        int u = preord[i];
        lint max1 = 0, max2 = 0;
        for (pil x : from[u]) {
            int v = x.first;
            if (v == par[u] || in_cyc[v]) continue;
            best[u] = max(best[u], best[v]);
            dp[u] = max(dp[u], dp[v] + x.second);
            lint val = dp[v] + x.second;
            if (val > max1) max2 = max1, max1 = val;
            else if (val > max2) max2 = val;
        }
        best[u] = max(best[u], max1 + max2);
    }
    return best[s];
}
 
vector<lint> lens;
lint len_sum;
void precomp() {
    if (cyc.size() == 2) {
        set<int> lens_set;
        for (int u : cyc) {
            for (pil x : from[u]) {
                int v = x.first;
                if (!in_cyc[v]) continue;
                lens_set.insert(x.second);
            }
        }
        lens.insert(lens.begin(), lens_set.begin(), lens_set.end());
        len_sum = lens[0] + lens[1];
        return;       
    }
 
    for (int i = 0; i < cyc.size(); i++) {
        int aft = (i + 1 == (int) cyc.size()) ? 0 : i + 1;
        int u = cyc[i], v = cyc[aft];
        for (pil x : from[u]) 
            if (x.first == v) lens.push_back(x.second), len_sum += x.second;
    }
}
 
lint comp() {
    multiset<lint> trans;
    vector<lint> val = {0};
    for (int i = 1; i < cyc.size(); i++) 
        val.push_back(val.back() + lens[i - 1]);
    for (int i = 1; i < cyc.size(); i++)
        val[i] = dp[cyc[i]] - val[i], trans.insert(val[i]);
    lint shift = 0;
        
    lint ans = 0;
    for (int i = 0; i < cyc.size(); i++) {
        ans = max(ans, dp[cyc[i]] + len_sum + *trans.rbegin() + shift);
        if (i + 1 == (int) cyc.size()) continue;
        trans.erase(trans.find(val[i + 1]));
        val[i] = dp[cyc[i]] - len_sum - shift;
        trans.insert(val[i]);
        shift += lens[i];
    }
    return ans;
}
 
int main() {
    // freopen("isl.in", "r", stdin), freopen("isl.out", "w", stdout);
    cin >> n;
    for (int u = 1; u <= n; u++) {
        cin >> to[u];
        lint len; cin >> len;
        from[to[u]].push_back({u, len});
    }
 
    lint ans = 0;
    for (int u = 1; u <= n; u++) {
        if (seen[u]) continue;
        cyc.clear(), lens.clear(), len_sum = 0;
        lint new_ans = 0;
        
        dfs1(u), dfs2(u);
        for (int u : cyc) new_ans = max(new_ans, dfs3(u));
        precomp();
        
        new_ans = max(new_ans, comp());
        reverse(cyc.begin(), cyc.end()), reverse(lens.begin(), next(lens.end(), -1));
        new_ans = max(new_ans, comp());
        ans += new_ans;
    }
    cout << ans << '\n';
}

Compilation message

islands.cpp: In function 'void precomp()':
islands.cpp:96:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   96 |     for (int i = 0; i < cyc.size(); i++) {
      |                     ~~^~~~~~~~~~~~
islands.cpp: In function 'lint comp()':
islands.cpp:107:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  107 |     for (int i = 1; i < cyc.size(); i++)
      |                     ~~^~~~~~~~~~~~
islands.cpp:109:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  109 |     for (int i = 1; i < cyc.size(); i++)
      |                     ~~^~~~~~~~~~~~
islands.cpp:114:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  114 |     for (int i = 0; i < cyc.size(); i++) {
      |                     ~~^~~~~~~~~~~~

Subtask #1
33.0 / 33.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 29136 KB Output is correct
2 Correct 5 ms 29016 KB Output is correct
3 Correct 5 ms 29020 KB Output is correct
4 Correct 5 ms 29188 KB Output is correct
5 Correct 5 ms 29192 KB Output is correct
6 Correct 4 ms 29128 KB Output is correct
7 Correct 5 ms 29020 KB Output is correct
8 Correct 4 ms 29020 KB Output is correct
9 Correct 5 ms 29020 KB Output is correct
10 Correct 4 ms 29020 KB Output is correct
11 Correct 6 ms 29064 KB Output is correct

Subtask #2
3.0 / 3.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 29212 KB Output is correct
2 Correct 5 ms 29184 KB Output is correct

Subtask #3
4.0 / 4.0

# Verdict Execution time Memory Grader output
1 Correct 7 ms 29276 KB Output is correct
2 Correct 8 ms 29532 KB Output is correct

Subtask #4
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 30044 KB Output is correct
2 Correct 31 ms 30180 KB Output is correct
3 Correct 24 ms 25312 KB Output is correct
4 Correct 26 ms 26292 KB Output is correct

Subtask #5
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 44 ms 31472 KB Output is correct
2 Correct 81 ms 32296 KB Output is correct

Subtask #6
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 110 ms 41404 KB Output is correct
2 Correct 203 ms 43608 KB Output is correct
3 Correct 262 ms 53964 KB Output is correct

Subtask #7
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 270 ms 53196 KB Output is correct
2 Correct 359 ms 70428 KB Output is correct
3 Correct 632 ms 75972 KB Output is correct
4 Correct 672 ms 91216 KB Output is correct

Subtask #8
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 482 ms 79212 KB Output is correct
2 Correct 1191 ms 120116 KB Output is correct
3 Correct 528 ms 72616 KB Output is correct
4 Correct 720 ms 102424 KB Output is correct
5 Correct 731 ms 102664 KB Output is correct
6 Correct 1054 ms 86612 KB Output is correct
7 Correct 1054 ms 131072 KB Output is correct

Subtask #9
0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 540 ms 97236 KB Output is correct
2 Correct 489 ms 92520 KB Output is correct
3 Runtime error 742 ms 131072 KB Execution killed with signal 9
4 Halted 0 ms 0 KB -