Submission #984169

#	Time	Username	Problem	Language	Result	Execution time	Memory
984169		stdfloat	Race (IOI11_race)	C++17	43 / 100	380 ms	262144 KiB

race

#include <bits/stdc++.h>
#include "race.h"
using namespace std;

using ll = long long;

#define ff  first
#define ss  second
#define pii pair<int, int>

int k, mn = INT_MAX;

vector<vector<int>> dp;

vector<vector<pii>> v, E;

void dfs(int x, int p = - 1) {
    dp[x][0] = 0;

    for (auto [i, w] : E[x])
        if (i != p) dfs(i, x);

    v.assign(k + 1, {});
    for (auto [i, w] : E[x]) {
        if (i == p) continue;

        for (int j = w; j <= k; j++) {
            if (dp[i][j - w] == INT_MAX) continue;

            if ((int)v[j].size() < 2) v[j].push_back({dp[i][j - w] + 1, i});
            else if (dp[i][j - w] + 1 < v[j][1].ff) v[j][1] = {dp[i][j - w] + 1, i};
            
            if ((int)v[j].size() == 2 && v[j][0].ff > v[j][1].ff) swap(v[j][0], v[j][1]);

            dp[x][j] = min(dp[x][j], dp[i][j - w] + 1);
        }
    }

    if (!v[k].empty()) mn = min(mn, (int)v[k][0].ff);
    for (int i = 1; i < k; i++) {
        if (v[i].empty() || v[k - i].empty()) continue;

        if (v[i][0].ss != v[k - i][0].ss) mn = min(mn, v[i][0].ff + v[k - i][0].ff);
        else if (1 < (int)v[k - i].size()) mn = min(mn, v[i][0].ff + v[k - i][1].ff);
    }
}

int best_path(int N, int K, int H[][2], int L[]) {
    E.assign(N, {});
    for (int i = 0; i < N - 1; i++) {
        E[H[i][0]].push_back({H[i][1], L[i]});
        E[H[i][1]].push_back({H[i][0], L[i]});
    }

    if (N <= (int)1e3) {
        for (int i = 0; i < N; i++) {
            queue<int> q;
            vector<int> cnt(N);
            vector<ll> dis(N, -1);
            q.push(i); dis[i] = 0;
            while (!q.empty()) {
                int x = q.front(); q.pop();

                for (auto [j, w] : E[x]) {
                    if (dis[j] == -1) {
                        q.push(j);
                        cnt[j] = cnt[x] + 1;
                        dis[j] = dis[x] + w;
                    }
                }
            }

            for (int j = 0; j < N; j++)
                if (dis[j] == K) mn = min(mn, cnt[j]);
        }
    }
    else {
        k = K;

        dp.assign(N, vector<int>(k + 1, INT_MAX));
        dfs(0);
    }

    return (mn == INT_MAX ? -1 : mn);
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 0 / 57