Submission #81767

#	Time	Username	Problem	Language	Result	Execution time	Memory
81767		chelly	Race (IOI11_race)	C++11	100 / 100	1909 ms	107748 KiB

race

#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
#define pb push_back
#define mp make_pair
const int MAXN = 200005, INF = 0x3f3f3f3f;

int N, K, H[MAXN][2], L[MAXN];
int sz[MAXN];
map<int, int> best;
bool done[MAXN];
vector<pii> adj[MAXN];
queue<pii> ar;
int ans = INF, target;
void dfs (int u, int p){
    sz[u]=1;
    for (pii e: adj[u]){
        if (e.first==p||done[e.first]) continue;
        dfs(e.first, u);
        sz[u]+=sz[e.first];
    }
}
int centroid (int u, int p, int S){
    for (pii e: adj[u]){
        if (sz[e.first]*2>S&&e.first!=p&&!done[e.first]) return centroid(e.first, u, S);
    }
    return u;
}
void path (int u, int p, int length, int cnt){
    if (length==target) ans = min(ans, cnt);
    else{
        ar.push(mp(length, cnt));
        if (best[target-length]!=0) ans = min(ans, best[target-length]+cnt);
    }
    for (pii e: adj[u]){
        if (e.first!=p&&!done[e.first]) path (e.first, u, length+e.second, cnt+1);
    }
}
void solve(int u){
    dfs(u, -1);
    u = centroid(u, -1, sz[u]);
    //cout<<u<<endl;
    best.clear();
    done[u] = true;
    for (pii e: adj[u]){
        if (done[e.first]) continue;
        path (e.first, u, e.second, 1);
        while (!ar.empty()){
            pii p = ar.front();
            ar.pop();
            if (best[p.first]==0) best[p.first] = p.second;
            else best[p.first] = min(best[p.first], p.second);
        }
    }
    for (pii e: adj[u]){
        if(!done[e.first]) solve(e.first);
    }
}
int best_path(int N, int K, int H[][2], int L[]){
    target = K;
    for (int i = 0; i<N-1; i++){
        adj[H[i][0]].pb(mp(H[i][1], L[i]));
        adj[H[i][1]].pb(mp(H[i][0], L[i]));
    }
    solve (0);
    return ans==INF?-1:ans;
}
/*
int main()
{
    cin>>N>>K;
    for (int i = 0; i<N-1; i++){
        scanf("%d%d%d", &H[i][0], &H[i][1], &L[i]);
    }
    cout<<best_path(N, K, H, L);
}*/

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