10034 - Freckles

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Observer
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10034 Help!

Post by Observer »

I'm a beginner in MST.

Could anyone give my some test cases for this problem. I keep getting WA...... :cry:

Thx in advance!
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Observer
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Post by Observer »

Finally I've got an AC...

However, I think my algorithm is too slow......

I use Kruskal's algorithm, however, I don't know how to check wheter the two endpoints of each line are disconnected effectively......

So, can anyone help me?? Thx!!
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Dominik Michniewski
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Post by Dominik Michniewski »

Union-find algorithm

DM
If you really want to get Accepted, try to think about possible, and after that - about impossible ... and you'll get, what you want ....
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Observer
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Post by Observer »

Could you give me more details, plz?

I often used Adjacency Matrix to solve graph problems, but it seems slow......
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Post by Dominik Michniewski »

try on google

idea is simple :
1. create vector of such number of elements (or table) of graph (nodes)
2. initialize all elements to our number (i.e. 1,2,3 .... for node 1,2,3 ...)
3, for each added edge update values in such way, that to groups of nodes, which are separate earlier join in one group

example:
nodes 1,2,3,4,5
edges 12,14,53
table: 1,2,3,4,5
step 3. edge 12 table (after) : 1,1,3,4,5
step 3. edge 14 table (after) : 1,1,3,1,5
step 3. edge 53 table (after) : 1,1,3,1,3
and so on :)
time complexity is O(E*V) and is better than using adjacency matrix which is typical O(V^3)

Best regards
DM
If you really want to get Accepted, try to think about possible, and after that - about impossible ... and you'll get, what you want ....
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Observer
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Post by Observer »

Thx for your help!

However, I still don't quite get it.....

I tried to search Google for related information. However, most of it is uninterpretable by me...... >_<


Can anyone explain it more clearly plz?? Any help is appreciated! :P :P
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Observer
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Post by Observer »

(Edited)

Plz see if what you mean is as follows, Dominik:

Let every edge be X -> Y, where X > Y.

Step 1: Initialization
- Then we have the following array: 1 2 3 4 5 ...

Step 2:
For each edge do \\ for MST, check if array[X] <> array[Y]
- for each node do
-- if array[node] == array[X]
--- then array[node] = array[Y]

Step 3:
All edge is connected when every cell of the array is 1.

Is it correct? Plz reply. Thx!
Last edited by Observer on Thu Jun 12, 2003 5:46 pm, edited 1 time in total.
7th Contest of Newbies
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Time: 12:00 - 16:00 (UTC)
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Post by Dominik Michniewski »

No.

let edge X->Y, you cannot make any assumption to x and y. our goal is making equal values in table.

so.
if table[x] != table[y] <- that means group of nodes to which belongs x is different of group of nodes to which belongs y />
let z = table[x]
change every table[x] == z to table[y]

after step 2, we have number of groups (disjoint) ...

DM
If you really want to get Accepted, try to think about possible, and after that - about impossible ... and you'll get, what you want ....
Born from ashes - restarting counter of problems (800+ solved problems)

Observer
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Post by Observer »

Thx!! With your help, I've got accepted in much shorter time!!!

However, I'm still getting WA in Q10397......

Anyway, Thx a lot!!


Btw, any help on that one too? Thx!
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Towhid
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10034 input

Post by Towhid »

Can someone provide an critical input set for the problem?
From 0 to 0

titid_gede
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Post by titid_gede »

i dont have any critical inputs, but i can give you a hint, since i think your problem's same than mine...
hint : only use sqrt when necessary.. do not use sqrt if you can avoid it. hope it can help.

-titid-
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b3yours3lf
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10034 - Freckles

Post by b3yours3lf »

i use kruskal to solve this problem, but a got WA many times...
Last edited by b3yours3lf on Wed Oct 22, 2003 10:05 am, edited 1 time in total.

titid_gede
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Post by titid_gede »

hmmm... you dont even pass the sample input output :)
at first look, your sort function seems to be incorrect :)
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b3yours3lf
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Post by b3yours3lf »

sorry, i've post wrong code, here is the correct one
[c]
--cut--
[/c]
Last edited by b3yours3lf on Mon Oct 27, 2003 5:42 am, edited 1 time in total.

Grinder
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Post by Grinder »

b3yours3lf u will edit this.
for(k=0;k<n;k++)
{
if(set[k]==set[e[j].v2])
set[k]=set[e[j].v1];
}
as
for(k=0;k<n;k++)
{
if(set[k]==set[e[j].v1)
set[k]=set[e[j].v2];
}
may be u will got AC :D
I hate three things one- Wrong Answer,TL and the problem which statement is not clear.

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