Submission #525758

#	Time	Username	Problem	Language	Result	Execution time	Memory
525758		mjhmjh1104	Mountains and Valleys (CCO20_day1problem3)	C++17	11 / 25	699 ms	108484 KiB

Main

#include <cstdio>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;

int n, m, dp[20][20971520];
vector<int> tree[200006];
vector<pair<int, int>> adj[200006];

int f(int x, int y) {
    if (dp[x][y] + 1) return dp[x][y];
    if (!y) return dp[x][y] = 0;
    dp[x][y] = (int)1e9;
    for (auto &i: adj[x]) dp[x][y] = min(dp[x][y], i.second + f(i.first, y & ~(1 << i.first)));
    for (auto &i: tree[x]) dp[x][y] = min(dp[x][y], 1 + f(i, y & ~(1 << i)));
    return dp[x][y];
}

int lt[5006][5006], dist[200006], par[200006], sz[200006];
bool cl[200006];

void dfs_lt(int x, int y, int dist = 0, int prev = -1) {
    lt[y][x] = dist;
    for (auto &i: tree[x]) if (i != prev) dfs_lt(i, y, dist + 1, x);
}

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 dfs_dist(int x, int prev = -1) {
    int ret = x;
    for (auto &i: tree[x]) if (i != prev) {
        dist[i] = 1 + dist[x];
        int t = dfs_dist(i, x);
        if (dist[t] > dist[ret]) ret = t;
    }
    return ret;
}

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 });
        }
    }
    if (n <= 20) {
        for (int i = 0; i < n; i++) for (int j = 0; j < 1 << n; j++) dp[i][j] = -1;
        int res = (int)1e9;
        for (int i = 0; i < n; i++) res = min(res, f(i, (1 << n) - 1 ^ 1 << i));
        printf("%d", res);
        return 0;
    }
    for (int i = 0; i < n; i++) dfs_lt(i, i);
    int t = dfs_dist(dist[0] = 0);
    dist[t] = 0;
    int s = dfs_dist(t);
    int zero = 2 * (n - 1) - dist[s], one = (int)1e9;
    if (n <= 1000) for (int i = 0; i < n; i++) for (auto &j: adj[i]) if (i < j.first) {
        int curr = j.second + 2 * (n - 1) - lt[i][j.first] - 1;
        dfs(j.first);
        int x = i, pv = -1;
        vector<int> v;
        int y = -1;
        while (x != -1) {
            v.emplace_back();
            vector<int> curr;
            for (auto &i: tree[x]) if (i != pv && i != par[x]) {
                v.back() = max(v.back(), sz[i]);
                curr.push_back(sz[i]);
            }
            sort(curr.rbegin(), curr.rend());
            if (!curr.empty()) y = max(y, curr[0]);
            if ((int)curr.size() > 1) y = max(y, curr[0] + curr[1] - 1);
            pv = x;
            x = par[x];
        }
        for (int i = 0; i < (int)v.size(); i++) for (int j = i + 1; j < (int)v.size(); j++) y = max(y, v[i] + v[j] - (j - i - 1));
        curr -= y;
        one = min(one, curr);
    }
    printf("%d", min(zero, one));
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:63:66: warning: suggest parentheses around arithmetic in operand of '^' [-Wparentheses]
   63 |         for (int i = 0; i < n; i++) res = min(res, f(i, (1 << n) - 1 ^ 1 << i));
      |                                                         ~~~~~~~~~^~~
Main.cpp:48:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:51:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   51 |         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: 0 / 2
• Subtask 6: 0 / 3
• Subtask 7: 0 / 5
• Subtask 8: 0 / 4