Submission #39846

#	Time	Username	Problem	Language	Result	Execution time	Memory
39846		MladenP	Network (BOI15_net)	C++14	100 / 100	826 ms	69388 KiB

net

#include<bits/stdc++.h>
#define STIZE(x) fprintf(stderr, "STIZE%d\n", x);
#define PRINT(x) fprintf(stderr, "%s = %d\n", #x, x);
#define NL(x) printf("%c", " \n"[(x)]);
#define lld long long
#define pii pair<int,int>
#define pb push_back
#define fi first
#define se second
#define all(a) begin(a),end(a)
#define sz(a) int((a).size())
#define LINF LLONG_MAX
#define INF INT_MAX
#define EPS 1e-9
using namespace std;
#define MAXN 500010
int n, root, centroid;
int deg[MAXN];
int brlist[MAXN], cntLeaf;
bool is_leaf[MAXN];
vector<int> adj[MAXN];
int dfs1(int cur, int pret) {
    if(brlist[cur] != 0) return brlist[cur];
    if(is_leaf[cur]) return brlist[cur] = 1;
    for(auto x : adj[cur]) {
        if(x != pret) brlist[cur] += dfs1(x, cur);
    }
    return brlist[cur];
}
int dfs2(int cur, int pret) {
    int maxi = 0;
    for(auto x : adj[cur]) {
        if(!is_leaf[x] && brlist[x] >= brlist[maxi] && x != pret) maxi = x;
    }
    if(brlist[maxi] > cntLeaf-cntLeaf/2) return dfs2(maxi, cur);
    else return cur;
}
int susedi;
vector<int> lisce[MAXN];
void dfs3(int cur, int pret) {
    if(is_leaf[cur]) {
        lisce[susedi].pb(cur);
        return;
    }
    for(auto x : adj[cur]) {
        if(x != pret) dfs3(x, cur);
        if(cur == centroid) susedi++;
    }
}
priority_queue<pii> pq;
int main() {
    scanf("%d", &n);
    if(n <= 2) return printf("1\n1 %d", n), 0;
    for(int i = 0; i < n-1; i++) {
        int x, y; scanf("%d%d", &x, &y);
        adj[x].pb(y);
        adj[y].pb(x);
        deg[x]++; deg[y]++;
    }
    for(int i = 1; i <= n; i++) {
        if(deg[i] == 1) is_leaf[i] = 1, cntLeaf++;
        else root = i;
    }
    dfs1(root, 0);
    centroid = dfs2(root, 0);
    dfs3(centroid, 0);
    for(int i = 0; i < susedi; i++) {
        pq.push({sz(lisce[i]), i});
    }
    printf("%d\n", cntLeaf-cntLeaf/2);
    while(sz(pq) > 1) {
        pii vrh1 = pq.top(); pq.pop();
        pii vrh2 = pq.top(); pq.pop();
        int komp1 = vrh1.se, komp2 = vrh2.se;
        int rep1 = vrh1.fi, rep2 = vrh2.fi;
        printf("%d %d\n", lisce[komp1][--rep1], lisce[komp2][--rep2]);
        if(rep1) pq.push({rep1, komp1});
        if(rep2) pq.push({rep2, komp2});
    }
    if(pq.size() == 1) {
        int komp = pq.top().se;
        printf("%d %d\n", lisce[komp][0], centroid);
    }
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:52:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
                    ^
net.cpp:55:40: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         int x, y; scanf("%d%d", &x, &y);
                                        ^

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 37 / 37