## 10765 - Doves and bombs

All about problems in Volume 107. If there is a thread about your problem, please use it. If not, create one with its number in the subject.

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christephan
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Posts: 5
Joined: Fri Jan 25, 2008 9:27 pm

### 10765 - Doves and bombs

My O(n^2) algorithm (DFS+heap) got TLE.

Any better solutions? THX.

christephan
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Posts: 5
Joined: Fri Jan 25, 2008 9:27 pm
I think I was sleepy..

When I get up today, I add backtracking to my DFS algorithm such that I can prevent re-calculating as much as posibble.
The algorithm now may be O(|E| + |V| log |V|), I'm not sure. (n log n is for heap sort), where |E| <= 10 |V|.

Then now AC with 0.03s

ngchumin
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Posts: 8
Joined: Sun Jun 16, 2002 11:18 am

### 10765 Doves and bombs

Hi, i keeping getting WA even though i tried on my inputs i devised myself. Any one able to help with any input cases?

Thanks alot!

nbacool2
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Posts: 24
Joined: Fri Jul 25, 2014 4:31 pm

### Re: 10765 - Doves and bombs

OK, I make a standard implementation of finding the articulation points with a DFS. Got correct output on the sample test cases and other I made up myseld but I still get WA. Any ideas?

Code: Select all

``````#include <iostream>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <cstdio>
#include <utility>
using namespace std;
struct Station
{
int number, pigeonValue;
Station(int n = 0, int p = 0)
{
number = n;
pigeonValue = p;
}
bool operator < (const Station &other) const
{
if(pigeonValue == other.pigeonValue) return number < other.number;
return pigeonValue > other.pigeonValue;
}
};
const int MAXN = 10001;
int N, M;
vector<int> G[MAXN];
int parent[MAXN];
bool visited[MAXN];
int DFSRoot;
int rootChildren;
bool articulationPoint[MAXN];
int pigeonValue[MAXN];
int numberOfTreeChildren[MAXN];
int dfs_num[MAXN];
int dfs_low[MAXN];
int counter;
vector<vector<Station> > answers;
int DFS(int root)
{
visited[root] = true;
dfs_num[root] = counter;
dfs_low[root] = counter;
++counter;
int nodes = 0;
int SCCs = 0;
for(int i = 0; i < G[root].size(); ++i)
{
int child = G[root][i];
if(!visited[child])
{
++numberOfTreeChildren[root];
if(root == DFSRoot) ++rootChildren;
parent[child] = root;
nodes += DFS(child);
if(dfs_low[child] >= dfs_num[root])
{
//cout<<root<<" is critical. Adding "<<child<<" as a root of a parent SCC\n";
articulationPoint[root] = true;
++SCCs;
}
dfs_low[root] = min(dfs_low[root], dfs_low[child]);
}
else if(child != parent[root])
{
dfs_low[root] = min(dfs_low[root], dfs_num[child]);
}
}
if(articulationPoint[root])
{
if(root != DFSRoot) ++SCCs;
pigeonValue[root] = SCCs;
}
return nodes + 1;
}
void read()
{
for(int i = 0; i < MAXN; ++i) G[i].clear();
memset(parent, -1, sizeof parent);
memset(visited, 0, sizeof visited);
memset(articulationPoint, 0, sizeof articulationPoint);
memset(pigeonValue, 0, sizeof pigeonValue);
memset(numberOfTreeChildren, 0, sizeof numberOfTreeChildren);
counter = 0;
//now do shit
while(true)
{
int from, to;
cin >> from >> to;
if(from == -1 && to == -1) break;
G[from].push_back(to);
G[to].push_back(from);
}
for(int i = 0; i < N; ++i)
{
if(!visited[i])
{
DFSRoot = i;
rootChildren = 0;
int nodeCount = DFS(i);
if(rootChildren > 1)
{
articulationPoint[i] = true;
pigeonValue[i] = numberOfTreeChildren[i];
}
}
}
//cout<<"Articulation points are:\n";
vector<Station> stations;
for(int i = 0; i < N; ++i)
{
if(articulationPoint[i])
{
stations.push_back(Station(i, pigeonValue[i]));
//cout<<i<<" "<<pigeonValue[i]<<endl;
}
}
//cout<<"END";
sort(stations.begin(), stations.end());
stations.resize(M);
answers.push_back(stations);
}
int main()
{
ios::sync_with_stdio(false);
while(true)
{
cin >> N >> M;
if(N == 0 && M == 0) break;
read();
}
//cout<<"RESULT:\n";
for(int i = 0; i < answers.size(); ++i)
{
for(int j = 0; j < answers[i].size(); ++j)
{
cout<<answers[i][j].number<<" "<<answers[i][j].pigeonValue<<'\n';
}
if(i < answers.size()-1)cout<<'\n';
}
return 0;
}
``````

brianfry713
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Posts: 5947
Joined: Thu Sep 01, 2011 9:09 am
Location: San Jose, CA, USA

### Re: 10765 - Doves and bombs

Print a blank line after the output for each set of input, including the last one.
Check input and AC output for thousands of problems on uDebug!

nbacool2
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Posts: 24
Joined: Fri Jul 25, 2014 4:31 pm

### Re: 10765 - Doves and bombs

With and without printing the additional blank line afer the last test case I still get WA :/

brianfry713
Guru
Posts: 5947
Joined: Thu Sep 01, 2011 9:09 am
Location: San Jose, CA, USA

### Re: 10765 - Doves and bombs

Post your updated code.
Check input and AC output for thousands of problems on uDebug!

just_yousef
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Posts: 50
Joined: Tue Dec 17, 2013 11:01 pm

### Re: 10765 - Doves and bombs

Never mind I found the bug