| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 25726 | gs14004 | Pipes (CEOI15_pipes) | C++11 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
typedef pair<int,int> pi;
struct disj{
int pa[100005];
void init(int n){
for(int i=0; i<=n; i++) pa[i] = i;
}
int find(int x){
return pa[x] = (pa[x] == x ? x : find(pa[x]));
}
bool uni(int p, int q){
p = find(p);
q = find(q);
if(p == q) return 0;
pa[q] = p;
find(q);
return 1;
}
}disj1, disj2;
int n, m;
vector<pi> tree, bri;
vector<int> graph[100005];
int par[100005][17], dep[100005];
bool vis[100005];
void dfs(int x, int pa){
vis[x] = 1;
par[x][0] = pa;
for(int i=1; i<17; i++){
par[x][i] = par[par[x][i-1]][i-1];
}
for (auto &i : graph[x]){
if(i == pa) continue;
dep[i] = dep[x] + 1;
dfs(i,x);
}
}
int lca(int x, int y){
if(dep[x] < dep[y]) swap(x,y);
int dx = dep[x] - dep[y];
for(int i=0; i<17; i++){
if((dx >> i) & 1) x = par[x][i];
}
for(int i=16; i>=0; i--){
if(par[x][i] != par[y][i]){
x = par[x][i];
y = par[y][i];
}
}
if(x != y) x = par[x][0];
return x;
}
int up[100005];
void dfs2(int x, int pa){
for (auto &i : graph[x]){
if(i == pa) continue;
dfs2(i,x);
up[x] = max(up[x], up[i] - 1);
}
if(pa != 0 && up[x] == 0) printf("%d %d\n",pa,x);
}
int main(){
scanf("%d %d\n",&n,&m);
disj1.init(n);
disj2.init(n);
while(m--){
int u = 0, v = 0;
char str[15];
fgets(str,15,stdin);
int pos = 0;
while(str[pos] != ' '){
u = (10 * u) + (str[pos] - '0');
pos++;
}
pos++;
while(str[pos] != '\n' && str[pos]){
v = (10 * v) + (str[pos] - '0');
pos++;
}
if(disj1.uni(u,v)){
tree.push_back(pi(u,v));
}
else if(disj2.uni(u,v)){
bri.push_back(pi(u,v));
}
}
for(auto &i : tree){
graph[i.first].push_back(i.second);
graph[i.second].push_back(i.first);
}
auto cmp = [&](const pi &a, const pi &b){
return disj1.find(a.first) < disj1.find(b.first);
};
sort(bri.begin(), bri.end(), cmp);
for(int i=1; i<=n; i++){
if(!vis[i]){
int pos = disj1.find(i);
dfs(pos,0);
int p = lower_bound(bri.begin(), bri.end(), pi(pos, -1), cmp) - bri.begin();
while(p < bri.end() && disj1.find(bri[p].first) != pos){
pi i = bri[p++];
int l = lca(i.first,i.second);
up[i.first] = max(up[i.first],dep[i.first] - dep[l]);
up[i.second] = max(up[i.second],dep[i.second] - dep[l]);
}
dfs2(pos,0);
}
}
}