Submission #525571

#	Time	Username	Problem	Language	Result	Execution time	Memory
525571		mjhmjh1104	Mountains and Valleys (CCO20_day1problem3)	C++17	3 / 25	1680 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], depth[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) {
        depth[i] = depth[x] + 1;
        sz[x] += dfs(i, x);
    }
    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 intersect(int x, int y, int z, int w) {
    int ret = 0;
    for (int i = 0; i < n; i++) cl[i] = false;
    if (depth[x] < depth[y]) swap(x, y);
    if (depth[z] < depth[w]) swap(z, w);
    while (depth[x] > depth[y]) {
        if (!cl[x]) ret++, cl[x] = true;
        x = par[x];
    }
    while (x != y) {
        if (!cl[x]) ret++, cl[x] = true;
        if (!cl[y]) ret++, cl[y] = true;
        x = par[x], y = par[y];
    }
    while (depth[z] > depth[w]) {
        if (!cl[z]) ret++, cl[z] = true;
        z = par[z];
    }
    while (z != w) {
        if (!cl[z]) ret++, cl[z] = true;
        if (!cl[w]) ret++, cl[w] = true;
        z = par[z], w = par[w];
    }
    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, two = (int)1e9;
    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(i);
        int x = j.first, pv = -1;
        vector<int> v;
        while (depth[x]) {
            v.emplace_back();
            for (auto &i: tree[x]) if (i != pv && i != par[x]) v.back() = max(v.back(), sz[i]);
            pv = x;
            x = par[x];
        }
        int y = *max_element(v.begin(), v.end());
        for (int i = 1; i < (int)v.size(); i++) y = max(y, v[i - 1] + v[i]);
        curr -= y;
        one = min(one, curr);
    }
    /*if (n <= 500) for (int i = 0; i < n; i++) for (auto &j: adj[i]) if (i < j.first) for (int k = 0; k < n; k++) for (auto &l: adj[k]) if (k < l.first) {
        two = min(two, j.second + l.second + 2 * (n - 1) - intersect(i, l.first, k, j.first));
        two = min(two, j.second + l.second + 2 * (n - 1) - intersect(i, k, l.first, j.first));
    }*/
    printf("%d", min({ zero, one, two }));
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:90:66: warning: suggest parentheses around arithmetic in operand of '^' [-Wparentheses]
   90 |         for (int i = 0; i < n; i++) res = min(res, f(i, (1 << n) - 1 ^ 1 << i));
      |                                                         ~~~~~~~~~^~~
Main.cpp:75:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   75 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:78:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   78 |         scanf("%d%d%d", &x, &y, &w);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~

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