Submission #63015

#	Time	Username	Problem	Language	Result	Execution time	Memory
63015		zubec	Race (IOI11_race)	C++14	100 / 100	1818 ms	80492 KiB

race

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

const int N = 200100;

vector <pair<int, int> > g[200100];

int needLen, n, sz[N], pr[N];
bool used[N];

int ans = 1e9;
map<int, int> mp1;

int fnd_cntr(int v, int p, int szcmp){
    int pos = -1;
    bool bb = 0;
    for (int i = 0; i < g[v].size(); i++){
        int to = g[v][i].first;
        if (to == p || used[to])
            continue;
        if (sz[to]-1 >= szcmp/2){
            bb = 1;
            pos = to;
            break;
        }
    }
    if (bb == 0)
        return v;
    return fnd_cntr(pos, v, szcmp);
}

void dfs1(int v, int p, int len, int pth){
    sz[v] = 1;
    pr[v] = p;
    if (mp1.find(needLen-len)!=mp1.end()){
        ans = min(ans, mp1[needLen-len]+pth);
    }
    for (int i = 0; i < g[v].size(); i++){
        int to = g[v][i].first, curlen = g[v][i].second;
        if (to == p || used[to])
            continue;
        dfs1(to, v, len+curlen, pth+1);
        sz[v] += sz[to];
    }
}

void dfs2(int v, int p, int len, int pth){
    if (mp1.find(len) != mp1.end())
        mp1[len] = min(mp1[len], pth); else
        mp1[len] = pth;
    for (int i = 0; i < g[v].size(); i++){
        int to = g[v][i].first, curlen = g[v][i].second;
        if (to == p || used[to])
            continue;
        dfs2(to, v, len+curlen, pth+1);
    }
}

void build(int v, int p){
    if (used[v])
        return;
    int cntr = fnd_cntr(v, pr[v], sz[v]);
    used[cntr] = 1;
    mp1[0] = 0;
    for (int i = 0; i < g[cntr].size(); i++){
        int to = g[cntr][i].first, len = g[cntr][i].second;
        if (used[to])
            continue;
        dfs1(to, 0, len, 1);
        dfs2(to, 0, len, 1);
    }
    if (mp1.find(needLen) != mp1.end())
        ans = min(ans, mp1[needLen]);
    mp1.clear();
    for (int i = 0; i < g[cntr].size(); i++){
        int to = g[cntr][i].first;
        if (!used[to])
            build(to, cntr);
    }
}

int best_path(int N, int K, int H[][2], int L[]){
    needLen = K;
    n = N;
    for (int i = 1; i < n; i++){
        int u = H[i-1][0], v = H[i-1][1], len = L[i-1];
        g[u].push_back({v, len});
        g[v].push_back({u, len});
    }
    dfs1(1, 0, 0, 0);
    mp1.clear();
    build(1, 0);
    if (ans == 1e9)
        ans = -1;
    return ans;
}

Compilation message (stderr)

race.cpp: In function 'int fnd_cntr(int, int, int)':
race.cpp:18:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < g[v].size(); i++){
                     ~~^~~~~~~~~~~~~
race.cpp: In function 'void dfs1(int, int, int, int)':
race.cpp:39:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < g[v].size(); i++){
                     ~~^~~~~~~~~~~~~
race.cpp: In function 'void dfs2(int, int, int, int)':
race.cpp:52:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < g[v].size(); i++){
                     ~~^~~~~~~~~~~~~
race.cpp: In function 'void build(int, int)':
race.cpp:66:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < g[cntr].size(); i++){
                     ~~^~~~~~~~~~~~~~~~
race.cpp:76:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < g[cntr].size(); i++){
                     ~~^~~~~~~~~~~~~~~~

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