Submission #1234252

#	Time	Username	Problem	Language	Result	Execution time	Memory
1234252		Jer	Duathlon (APIO18_duathlon)	C++20	10 / 100	1096 ms	21692 KiB

count_triplets

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int MAXN = 100005;
const int LOG = 20;

vector<int> con[MAXN];
vector<int> parent(MAXN);
vector<int> depth(MAXN);
vector<vector<int>> up(LOG, vector<int>(MAXN));
vector<int> component_nodes;
vector<bool> visited(MAXN);

int n, m;

void dfs(int u, int par)
{
    parent[u] = par;
    depth[u] = depth[par] + 1;
    visited[u] = true;
    component_nodes.push_back(u);

    for (int v : con[u])
        if (v != par && !visited[v])
            dfs(v, u);
}

void build_up_table()
{
    for (int u : component_nodes)
        up[0][u] = parent[u];

    for (int k = 1; k < LOG; ++k)
        for (int u : component_nodes)
            up[k][u] = up[k - 1][up[k - 1][u]];
}

int lca(int u, int v)
{
    if (depth[u] < depth[v])
        swap(u, v);

    for (int k = LOG - 1; k >= 0; --k)
        if (depth[u] - (1 << k) >= depth[v])
            u = up[k][u];

    if (u == v)
        return u;

    for (int k = LOG - 1; k >= 0; --k)
        if (up[k][u] != up[k][v])
            u = up[k][u], v = up[k][v];

    return parent[u];
}

int compute_distance(int u, int v)
{
    int anc = lca(u, v);
    return depth[u] + depth[v] - 2 * depth[anc];
}

int main()
{
    scanf("%d%d", &n, &m);
    int a, b;

    for (int i = 0; i < m; ++i)
    {
        scanf("%d%d", &a, &b);
        con[a].push_back(b);
        con[b].push_back(a);
    }

    ll total = 0;

    for (int i = 1; i <= n; ++i)
        if (!visited[i])
        {
            component_nodes.clear();
            depth[0] = -1; // so that root depth = 0
            dfs(i, 0);
            build_up_table();

            for (int x : component_nodes)
                for (int y : component_nodes)
                    if (x < y)
                    {
                        int d = compute_distance(x, y);
                        if (d >= 2)
                            total += d - 1;
                    }
        }

    printf("%lld\n", total * 2LL);
    return 0;
}

Compilation message (stderr)

count_triplets.cpp: In function 'int main()':
count_triplets.cpp:68:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
count_triplets.cpp:73:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |         scanf("%d%d", &a, &b);
      |         ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 5
• Subtask 2: 0 / 11
• Subtask 3: 0 / 8
• Subtask 4: 10 / 10
• Subtask 5: 0 / 13
• Subtask 6: 0 / 15
• Subtask 7: 0 / 20
• Subtask 8: 0 / 8
• Subtask 9: 0 / 10