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Competition Arena > Ethernet

Ethernet

SRM 622 · 2013-12-22 · by ltaravilse

SRM 622 · 2013-12-22 · by ltaravilse · Dynamic Programming
Class Name: Ethernet
Return Type: int
Method Name: connect
Arg Types: (vector<int>, vector<int>, int)
Problem Statement

Problem Statement

You have N computers numbered 0 through N-1. They are connected into a single network. The topology of the network is a tree. You are given its description as int[]s parent and dist. Each of the int[]s contains exactly N-1 elements. For each i between 0 and N-2, inclusive, there is a cable connecting computers i+1 and parent[i], and the length of that cable is dist[i].

You are also given an int maxDist with the following meaning: The distance between any two computers in the same network must not exceed maxDist. (The distance between two computers is defined as the total length of cable between them.) If this is currently not the case for your network, you have to divide it into several smaller networks.

Formally, it means that you need to choose the number K of smaller networks you will have. Then you need to assign each of your computers into exactly one of the K networks. The following properties must be satisfied:
  • Each of the K new networks must form a connected subtree of the original tree.
  • The diameter of each new network must be at most maxDist.
Return the smallest value of K for which it is possible to divide the original network into K new networks with the above properties.

Constraints

  • parent will contain between 1 and 50 elements, inclusive.
  • dist will contain the same number of elements as parent.
  • For each valid i, the i-th element of parent will be between 0 and i, inclusive.
  • Each element of dist will be between 1 and 500, inclusive.
  • maxDist will be between 1 and 500, inclusive.
Examples
0)
{0,0,0}
{1,1,1}
2
Returns: 1

The diameter of this network is 2, which is small enough.

1)
{0,0,0,0,0,0,0}
{1,2,3,4,5,6,7}
8
Returns: 4

One optimal solution: the new networks will be formed by computers {4}, {6}, {7}, and {0,1,2,3,5}.

2)
{0,1,2,3,4,5}
{1,2,3,4,5,6}
6
Returns: 3

One optimal solution is to put computers {0,1,2,3} into the first new network, {4,5} into the second one, and {6} will be the third network.

3)
{0,0,0,1,1}
{1,1,1,1,1}
2
Returns: 2

The two new networks can be {0,2,3} and {1,4,5}.

4)
{0}
{1}
1
Returns: 1

Submissions are judged against all 38 archived test cases, of which 5 are shown here. Case numbers match the judge’s.

Coding Area

Language: C++17 · define a public class Ethernet with a public method int connect(vector<int> parent, vector<int> dist, int maxDist) · 38 test cases · 2 s / 256 MB per case

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