146 lines
4.0 KiB
C++
146 lines
4.0 KiB
C++
/**
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* @file minimun_spanning_tree.cpp
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*/
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/*
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* This program source code file is part of KiCad, a free EDA CAD application.
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*
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* Copyright (C) 2011 Jean-Pierre Charras
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* Copyright (C) 2004-2011 KiCad Developers, see change_log.txt for contributors.
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*
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* derived from this article:
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* http://compprog.wordpress.com/2007/11/09/minimal-spanning-trees-prims-algorithm
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you may find one here:
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* http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
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* or you may search the http://www.gnu.org website for the version 2 license,
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* or you may write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
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*/
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#include <limits.h>
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#include <minimun_spanning_tree.h>
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#include <class_pad.h>
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/*
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* The class MIN_SPAN_TREE calculates the rectilinear minimum spanning tree
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* of a set of points (pads usually having the same net)
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* using the Prim's algorithm.
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*/
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/*
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* Prim's Algorithm
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* Step 0
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* Pick any vertex as a starting vertex. (Call it S).
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* Mark it with any given flag, say 1.
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*
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* Step 1
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* Find the nearest neighbour of S (call it P1).
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* Mark both P1 and the edge SP1.
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* cheapest unmarked edge in the graph that doesn't close a marked circuit.
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* Mark this edge.
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*
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* Step 2
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* Find the nearest unmarked neighbour to the marked subgraph
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* (i.e., the closest vertex to any marked vertex).
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* Mark it and the edge connecting the vertex.
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*
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* Step 3
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* Repeat Step 2 until all vertices are marked.
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* The marked subgraph is a minimum spanning tree.
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*/
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MIN_SPAN_TREE::MIN_SPAN_TREE()
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{
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MSP_Init( 0 );
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}
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void MIN_SPAN_TREE::MSP_Init( int aNodesCount )
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{
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m_Size = std::max( aNodesCount, 1 );
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inTree.clear();
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linkedTo.clear();
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distTo.clear();
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if( m_Size == 0 )
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return;
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// Reserve space in memory
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inTree.reserve( m_Size );
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linkedTo.reserve( m_Size );
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distTo.reserve( m_Size );
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// Initialize values:
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for( int ii = 0; ii < m_Size; ii++ )
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{
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// Initialise dist with infinity:
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distTo.push_back( INT_MAX );
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// Mark all nodes as NOT beeing in the minimum spanning tree:
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inTree.push_back( 0 );
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linkedTo.push_back( 0 );
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}
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}
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/* updateDistances(int target)
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* should be called immediately after target is added to the tree;
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* updates dist so that the values are correct (goes through target's
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* neighbours making sure that the distances between them and the tree
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* are indeed minimum)
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*/
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void MIN_SPAN_TREE::updateDistances( int target )
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{
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for( int ii = 0; ii < m_Size; ++ii )
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{
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if( !inTree[ii] ) // no need to evaluate weight for already in tree items
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{
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int weight = GetWeight( target, ii );
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if( (weight > 0) && (distTo[ii] > weight ) )
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{
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distTo[ii] = weight;
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linkedTo[ii] = target;
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}
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}
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}
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}
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void MIN_SPAN_TREE::BuildTree()
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{
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// Add the first node to the tree
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inTree[0] = 1;
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updateDistances( 0 );
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for( int treeSize = 1; treeSize < m_Size; ++treeSize )
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{
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// Find the node with the smallest distance to the tree
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int min = -1;
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for( int ii = 0; ii < m_Size; ++ii )
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{
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if( !inTree[ii] )
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{
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if( (min == -1) || (distTo[min] > distTo[ii]) )
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min = ii;
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}
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}
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inTree[min] = 1;
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updateDistances( min );
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}
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}
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