Submission #108680

#	Time	Username	Problem	Language	Result	Execution time	Memory
108680		crackersamdjam	Race (IOI11_race)	C++14	0 / 100	6 ms	5120 KiB

race

#include <bits/stdc++.h>
#define gc getchar_unlocked()
#define pc(x) putchar_unlocked(x)
template<typename T> void scan(T &x){x = 0;register bool _=0;register T c=gc;_=c==45;c=_?gc:c;while(c<48||c>57)c=gc;for(;c<48||c>57;c=gc);for(;c>47&&c<58;c=gc)x=(x<<3)+(x<<1)+(c&15);x=_?-x:x;}
template<typename T> void print(T n){register bool _=0;_=n<0;n=_?-n:n;char snum[65];int i=0;do{snum[i++]=n%10+48;n/= 10;}while(n);--i;if (_)pc(45);while(i>=0)pc(snum[i--]);pc(10);}
template<typename First, typename ... Ints>
void scan(First &arg, Ints&... rest){scan(arg);scan(rest...);}

using namespace std;
typedef pair<int, int> pii;
const int MM = 2e5+2;

int N, K, dis[MM], sz[MM], tot, len[MM], ans = INT_MAX;
bool vis[MM];
vector<pii> adj[MM];
unordered_map<int, int> cnt;

int getsz(int cur, int pre){
    sz[cur] = 1;
    for(auto &e: adj[cur]){
        if(e.first != pre && !vis[e.first])
            sz[cur] += getsz(e.first, cur);
    }
    return sz[cur];
}

int findcent(int cur, int pre){
    for(auto &e: adj[cur]){
        if(!vis[e.first] && e.first != pre && sz[e.first]*2 > tot)
            return findcent(e.first, cur);
    }
    return cur;
}

void dfs(int cur, int pre){
    
    for(auto &e: adj[cur]){
        if(e.first == pre || vis[e.first])
            continue;
        
        dis[e.first] = dis[cur] + e.second;
        len[e.first] = len[cur] + 1;
        dfs(e.first, cur);
    }
    
    //printf("add %d %d %d\n", cur, dis[cur], len[cur]);
    
    if(!cnt[dis[cur]])
        cnt[dis[cur]] = len[cur];
    else
        cnt[dis[cur]] = min(cnt[dis[cur]], len[cur]);
}

void go(int root){
    //printf("go %d\n", root);
    
    //works bc root is edge of tree
    //first time must start from endpt
    getsz(root, -1);
    tot = sz[root];
    
    if(sz[root] == 1)
        return;
    
    int cent = findcent(root, -1);
    //printf("cent %d\n", cent);
    
    cnt.clear();
    dis[cent] = 0;
    len[cent] = 0;
    dfs(cent, -1);
    
    for(auto u: cnt){
        //printf("u %d %d\n", u.first, u.second);
        if(u.first <= K and (cnt[K-u.first] or (u.first == K and cnt[K])))
            ans = min(ans, u.second + cnt[K-u.first]);
    }
    
    vis[cent] = 1;
    //block off
    
    for(auto u: adj[cent]){
        if(!vis[u.first])
            go(u.first);
    }
}

int best_path(int n, int k, int h[][2], int l[]){
    
    N = n, K = k;
    cout << n << " " << k << endl;
    
    for(int i = 0; i < N-1; i++){
        cout << h[i][0] << " " << h[i][1] << " " << l[i] << endl;
        adj[h[i][0]].push_back({h[i][1], l[i]});
        adj[h[i][1]].push_back({h[i][0], l[i]});
    }
    
    for(int i = 0; i < N; i++){
        if(adj[i].size() == 1){
            go(i);
            break;
        }
    }
    
    cout << ans << endl;
    return (ans == INT_MAX? -1: ans);
}

/*
#ifndef ONLINE_JUDGE

int main(){
    
    int h[][2] = {{0, 1}, {1, 2}, {1, 3}};
    int l[] = {1, 2, 4};
    
    int out = best_path(4, 3, h, l);
    print(out);
    
    return 0;
    /*
    int h[][2] = {{0, 1}, {1, 2}};
    int l[] = {1, 1};
    
    int out = best_path(3, 3, h, l);
    print(out == INT_MAX? -1: out);
    
    return 0;
    */
    /*
    int h[][2] = {{0, 1}, {0, 2}, {2, 3}, {3, 4}, {4, 5}, {0, 6}, {6, 7}, {6, 8}, {8, 9}, {8, 10}};
    int l[] = {3, 4, 5, 4, 6, 3, 2, 5, 6, 7};
    
    int out = best_path(11, 12, h, l);
    print(out == INT_MAX? -1: out);
    
    return 0;
     
}

#endif
*/
/*
 *
 * centroid decomp with map storing lengths from centroid (and min #)
 * check if two paths sum to K - linear
 * n log n
 */

Compilation message (stderr)

race.cpp:122:5: warning: "/*" within comment [-Wcomment]
     /*

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