Submission #525831

#	Time	Username	Problem	Language	Result	Execution time	Memory
525831		mjhmjh1104	Mountains and Valleys (CCO20_day1problem3)	C++17	16 / 25	7030 ms	29100 KiB

Main

#include <cstdio>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;
 
int n, m;
vector<int> tree[200006], child[200006];
vector<pair<int, int>> adj[200006];
int _par[200006], _sz[200006];
 
int dfs(int x, int prev = -1) {
    _par[x] = prev;
    _sz[x] = 1;
    for (auto &i: tree[x]) if (i != prev) {
        _sz[x] = max(_sz[x], dfs(i, x) + 1);
    }
    return _sz[x];
}

int dist[200006];
 
int dfs_dist(int x, int prev = -1) {
    vector<int> v;
    int ret = 0;
    dist[x] = 0;
    for (auto &i: tree[x]) if (i != prev) {
        v.push_back(dfs_dist(i, x) + 1);
        ret = max(ret, v.back());
        dist[x] = max(dist[x], dist[i]);
    }
    int v0 = max_element(v.begin(), v.end()) - v.begin();
    int X = v[v0];
    if (!v.empty()) v[v0] = 0;
    int v1 = max_element(v.begin(), v.end()) - v.begin();
    v[v0] = X;
    if (!v.empty()) dist[x] = max(dist[x], v[v0]);
    if ((int)v.size() > 1) dist[x] = max(dist[x], v[v0] + v[v1]);
    return ret;
}

int sz[200006], depth[200006], par[200006];
int in[200006], top[100006], T;

void dfs_child(int x, int prev = -1) {
    par[x] = prev;
    for (auto &i: tree[x]) if (i != prev) {
        child[x].push_back(i);
        dfs_child(i, x);
    }
}

int dfs_sz(int x) {
    sz[x] = 1;
    for (auto &i: child[x]) {
        depth[i] = depth[x] + 1;
        sz[x] += dfs_sz(i);
        if (sz[i] > sz[child[x][0]]) swap(child[x][0], i);
    }
    return sz[x];
}

void dfs_hld(int x) {
    in[x] = T++;
    for (auto &i: child[x]) {
        top[i] = (i == child[x][0] ? top[x] : i);
        dfs_hld(i);
    }
}

int get_dist(int u, int v) {
    int ret = 0;
    while (top[u] != top[v]) {
        if (depth[top[u]] < depth[top[v]]) swap(u, v);
        ret += depth[u] - depth[par[top[u]]];
        u = par[top[u]];
    }
    return ret + abs(depth[u] - depth[v]);
}

int main() {
    scanf("%d%d", &n, &m);
    while (m--) {
        int x, y, w;
        scanf("%d%d%d", &x, &y, &w);
        if (w == 1) {
            tree[x].push_back(y);
            tree[y].push_back(x);
        } else {
            adj[x].push_back({ y, w });
            adj[y].push_back({ x, w });
        }
    }
    dfs_child(0);
    dfs_sz(0);
    dfs_hld(0);
    dfs_dist(0);
    int zero = 2 * (n - 1) - dist[0], one = (int)1e9;
    for (int i = 0; i < n; i++) {
        dfs(i);
        dfs_dist(i);
        for (auto &j: adj[i]) if (i < j.first) {
            int curr = j.second + 2 * (n - 1) - get_dist(i, j.first) - 1;
            int x = j.first, pv = -1;
            vector<pair<int, int>> v;
            int y = -1, T = 0;
            while (x != -1) {
                for (auto &k: tree[x]) if (k != pv && k != _par[x]) {
                    if (_sz[k]) {
                        if (!v.empty() && v.back().second == T) {
                            y = max(y, v.back().first + _sz[k] - 1);
                            v.back().first = max(v.back().first, _sz[k]);
                        } else v.push_back({ _sz[k], T });
                    }
                    y = max(y, dist[k] - 1);
                }
                T++;
                pv = x;
                x = _par[x];
            }
            int ans = -(int)1e9;
            for (int i = 0; i < (int)v.size(); i++) {
                if (i) ans -= v[i].second - v[i - 1].second;
                y = max(y, ans + v[i].first + 1);
                ans = max(ans, v[i].first);
            }
            curr -= y;
            one = min(one, curr);
        }
    }
    printf("%d", min(zero, one));
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:82:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:85:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   85 |         scanf("%d%d%d", &x, &y, &w);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 1 / 1
• Subtask 2: 2 / 2
• Subtask 3: 2 / 2
• Subtask 4: 6 / 6
• Subtask 5: 2 / 2
• Subtask 6: 3 / 3
• Subtask 7: 0 / 5
• Subtask 8: 0 / 4