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Kruskal.cpp
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Kruskal.cpp
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//https://www.hackerearth.com/practice/algorithms/graphs/minimum-spanning-tree/tutorial/
#include "Kruskal.hpp"
#include <numeric>
//HACK
namespace
{
std::vector<EDGEID> skippedEdgeIds;
}
KruskalMST::KruskalMST(const std::vector<Node2D> &inputNodes) : nodes(inputNodes)
{
createEdges();
}
void KruskalMST::createEdges()
{
for(size_t i = 0; i < nodes.size(); ++i)
for(size_t j = i+1; j < nodes.size(); ++j)
{
edges.emplace_back(i,j,nodes);
}
auto edgeSort = [](const Edge &a, const Edge &b) -> bool
{
return a.w < b.w;
};
std::sort(edges.begin(), edges.end(), edgeSort);
edgeIds.resize(edges.size());
std::iota(edgeIds.begin(), edgeIds.end(), 0);
visited.resize(nodes.size(), false);
numVisited = 0;
curEdgeId = 0;
}
//Find root of graph all joining become the same id ?
ID KruskalMST::root(ID x)
{
while(edgeIds[x] != x)
{
edgeIds[x] = edgeIds[edgeIds[x]];
x = edgeIds[x];
}
return x;
}
//connect the edges to each other union1 in tutorial
void KruskalMST::join(ID x, ID y)
{
ID p = root(x);
ID q = root(y);
edgeIds[p] = edgeIds[q];
}
bool KruskalMST::isDone()
{
if(chosenEdges.size() != nodes.size()-1)
return false;
for(unsigned int i = 1; i < chosenEdges.size(); ++i)
if(edgeIds[i] != edgeIds[0])
return false;
return true;
}
//FIX THE EXIT CONDITION
//Done when root is same for all... 0-nodes.size()-1
void KruskalMST::genMST()
{
for(size_t i = 0; i < edges.size(); ++i)
{
//Show the edge considering
if(root(edges[i].a) != root(edges[i].b))
{
join(edges[i].a,edges[i].b);
if(!visited[edges[i].a])
{
visited[edges[i].a] = true;
++numVisited;
}
if(!visited[edges[i].b])
{
visited[edges[i].b] = true;
++numVisited;
}
chosenEdges.emplace_back(edges[i]);
//show closeEdges
if(isDone())
break;
}
//HACK
else
skippedEdgeIds.emplace_back(i);
}
//chosenEdges.insert(chosenEdges.end(),skippedEdgeIds.begin(),skippedEdgeIds.end());
//for(EDGEID i : skippedEdgeIds)
// chosenEdges.emplace_back(edges[skippedEdgeIds[i]]);
// chosenEdges.emplace_back(edges[skippedEdgeIds[i]]);//add loops ???
}
bool KruskalMST::stepMST()
{
if(isDone())
{
static bool T = true;
if(T)
for(EDGEID i : skippedEdgeIds)
chosenEdges.emplace_back(edges[skippedEdgeIds[i]]);
if(T)
{
T = false;
return true;
}
return false;
}
if(curEdgeId < edges.size())
{
ID i = curEdgeId;
if(root(edges[i].a) != root(edges[i].b))
{
join(edges[i].a,edges[i].b);
if(!visited[edges[i].a])
{
visited[edges[i].a] = true;
++numVisited;
}
if(!visited[edges[i].b])
{
visited[edges[i].b] = true;
++numVisited;
}
chosenEdges.emplace_back(edges[i]);
}
}
else
skippedEdgeIds.emplace_back(curEdgeId);
++curEdgeId;
return true;
}