Submission #672938

#	Time	Username	Problem	Language	Result	Execution time	Memory
672938		vuavisao	Hotspot (NOI17_hotspot)	C++14	38 / 100	1 ms	724 KiB

hotspot

#include<bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define ll long long
using namespace std;

const int N = 5e3 + 10;

int n, m, q;
vector<int> g[N];

int Lg, dist[N], parent[20][N];
int f[N];

void dfs(int u);
void dfs(int u) {
    for(const auto& v : g[u]) {
        if(v == parent[0][u]) continue;
        dist[v] = dist[u] + 1;
        parent[0][v] = u;
        dfs(v);
    }
}

int lca(int u, int v);
int lca(int u, int v) {
    if(dist[u] < dist[v]) swap(u, v);
    int delta = dist[u] - dist[v];
    for(int i = Lg; i >= 0; -- i) {
        if(delta >> i & 1) u = parent[i][u];
    }
    if(u == v) return u;
    for(int i = Lg; i >= 0; -- i) {
        if(parent[i][u] == parent[i][v]) continue;
        u = parent[i][u];
        v = parent[i][v];
    }
    return parent[0][u];
}

void dfs_finally(int u);
void dfs_finally(int u) {
    for(const auto& v : g[u]) {
        if(v == parent[0][u]) continue;
        dfs_finally(v);
        f[u] += f[v];
    }
}

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    if (fopen("NOI17_hotspot.inp", "r")) {
        freopen("NOI17_hotspot.inp", "r", stdin);
        freopen("NOI17_hotspot.out", "w", stdout);
    }
    cin >> n >> m;
    if(m != n - 1) assert(false);
    for(int i = 2; i <= n; ++ i) {
        int u, v; cin >> u >> v;
        ++ u; ++ v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    dist[1] = 1; dfs(1);
    Lg = __lg(n);
    for(int j = 1; j <= Lg; ++ j) {
        for(int i = 1; i <= n; ++ i) {
            parent[j][i] = parent[j - 1][parent[j - 1][i]];
        }
    }
    cin >> q;
    while(q-- > 0) {
        int u, v; cin >> u >> v;
        ++ u; ++ v;
        int anc = lca(u, v);
        ++ f[u]; ++ f[v];
        -- f[anc]; -- f[parent[0][anc]];
    }
    dfs_finally(1);
    cout << max_element(f + 1, f + 1 + n) - f - 1;
    return 0;
}

/// Code by vuavisao

Compilation message (stderr)

hotspot.cpp: In function 'int32_t main()':
hotspot.cpp:55:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   55 |         freopen("NOI17_hotspot.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
hotspot.cpp:56:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   56 |         freopen("NOI17_hotspot.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 4 / 4
• Subtask 2: 5 / 5
• Subtask 3: 11 / 11
• Subtask 4: 18 / 18
• Subtask 5: 0 / 26
• Subtask 6: 0 / 36