llvm-6502/lib/Transforms/Instrumentation/MaximumSpanningTree.h
2009-09-04 12:34:44 +00:00

96 lines
3.0 KiB
C++

//===- llvm/Analysis/MaximumSpanningTree.h - Interface ----------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This module privides means for calculating a maximum spanning tree for a
// given set of weighted edges. The type parameter T is the type of a node.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
#define LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
#include "llvm/ADT/EquivalenceClasses.h"
#include <vector>
#include <algorithm>
namespace llvm {
/// MaximumSpanningTree - A MST implementation.
/// The type parameter T determines the type of the nodes of the graph.
template <typename T>
class MaximumSpanningTree {
// A comparing class for comparing weighted edges.
template <typename CT>
struct EdgeWeightCompare {
bool operator()(typename MaximumSpanningTree<CT>::EdgeWeight X,
typename MaximumSpanningTree<CT>::EdgeWeight Y) const {
if (X.second > Y.second) return true;
if (X.second < Y.second) return false;
return false;
}
};
public:
typedef std::pair<const T*, const T*> Edge;
typedef std::pair<Edge, double> EdgeWeight;
typedef std::vector<EdgeWeight> EdgeWeights;
protected:
typedef std::vector<Edge> MaxSpanTree;
MaxSpanTree MST;
public:
static char ID; // Class identification, replacement for typeinfo
/// MaximumSpanningTree() - Takes a vector of weighted edges and returns a
/// spanning tree.
MaximumSpanningTree(EdgeWeights &EdgeVector) {
std::stable_sort(EdgeVector.begin(), EdgeVector.end(), EdgeWeightCompare<T>());
// Create spanning tree, Forest contains a special data structure
// that makes checking if two nodes are already in a common (sub-)tree
// fast and cheap.
EquivalenceClasses<const T*> Forest;
for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
Edge e = (*EWi).first;
Forest.insert(e.first);
Forest.insert(e.second);
}
// Iterate over the sorted edges, biggest first.
for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
Edge e = (*EWi).first;
if (Forest.findLeader(e.first) != Forest.findLeader(e.second)) {
Forest.unionSets(e.first, e.second);
// So we know now that the edge is not already in a subtree, so we push
// the edge to the MST.
MST.push_back(e);
}
}
}
typename MaxSpanTree::iterator begin() {
return MST.begin();
}
typename MaxSpanTree::iterator end() {
return MST.end();
}
};
} // End llvm namespace
#endif