Submission #998148

#	Time	Username	Problem	Language	Result	Execution time	Memory
998148		alexdumitru	Race (IOI11_race)	C++14	21 / 100	112 ms	27476 KiB

race

#include "race.h"
#include <iostream>
#include <vector>

using namespace std;

const int NMAX = 1e5;
const int KMAX = 1e6;

vector<pair<int, int>> g[NMAX];
int w[NMAX];
bool used[NMAX];
int minDepth[KMAX + 1];
int Ans;

int get_w(int node, int dad) {
    w[node] = 1;
    for (auto it : g[node]) {
        if (it.first == dad || used[it.first]) continue;
        get_w(it.first, node);
        w[node] += w[it.first];
    }
    return w[node];
}

int get_centroid(int node, int dad, int totalW) {
    for (auto it : g[node]) {
        if (it.first == dad || used[it.first]) continue;
        if (w[it.first] > totalW / 2)
            return get_centroid(it.first, node, totalW);
    }
    return node;
}

void dfs_add(int node, int dad, int k, int length, int depth) {
    if (length > k) return;
    minDepth[length] = min(minDepth[length], depth);

    for (auto it : g[node]) {
        if (it.first == dad || used[it.first]) continue;
        dfs_add(it.first, node, k, length + it.second, depth + 1);
    }
}

void dfs_compute(int node, int dad, int k, int length, int depth) {
    if (length > k) return;
    Ans = min(Ans, depth + minDepth[k - length]);

    for (auto it : g[node]) {
        if (it.first == dad || used[it.first]) continue;
        dfs_compute(it.first, node, k, length + it.second, depth + 1);
    }
}

void dfs_clear(int node, int dad, int k, int length) {
    if (length > k) return;
    minDepth[length] = NMAX;

    for (auto it : g[node]) {
        if (it.first == dad || used[it.first]) continue;
        dfs_clear(it.first, node, k, length + it.second);
    }
}

void go(int node, int k) {
    int totalW = get_w(node, -1);
    int c = get_centroid(node, -1, totalW);
    used[c] = true;

    minDepth[0] = 0;

    for (auto it : g[c]) {
        if (used[it.first]) continue;
        dfs_compute(it.first, -1, k, it.second, 1);
        dfs_add(it.first, -1, k, it.second, 1);
    }

  	dfs_clear(c, -1, k, 0);

    for (auto it : g[c])
        if (!used[it.first])
            go(it.first, k);
}

int best_path(int N, int K, int H[][2], int L[]) {
    Ans = N;

    for (int i = 0; i <= KMAX; i++) {
        minDepth[i] = N + 1;
    }

    for (int i = 0; i < N - 1; i++) {
        g[H[i][0]].emplace_back(H[i][1], L[i]);
        g[H[i][1]].emplace_back(H[i][0], L[i]);
    }

    go(0, K);

    return Ans == N ? -1 : Ans;
}

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