MaximumSpanningTree.h revision 68eca1aeb53324309e2cc7ec68a91423ec2e41e3 
1//===- llvm/Analysis/MaximumSpanningTree.h - Interface ----------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This module privides means for calculating a maximum spanning tree for a
11// given set of weighted edges. The type parameter T is the type of a node.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
16#define LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
17
18#include "llvm/ADT/EquivalenceClasses.h"
19#include <vector>
20#include <algorithm>
21
22namespace llvm {
23
24  /// MaximumSpanningTree - A MST implementation.
25  /// The type parameter T determines the type of the nodes of the graph.
26  template <typename T>
27  class MaximumSpanningTree {
28
29    // A comparing class for comparing weighted edges.
30    template <typename CT>
31    struct EdgeWeightCompare {
32      bool operator()(typename MaximumSpanningTree<CT>::EdgeWeight X,
33                      typename MaximumSpanningTree<CT>::EdgeWeight Y) const {
34        if (X.second > Y.second) return true;
35        if (X.second < Y.second) return false;
36        return false;
37      }
38    };
39
40  public:
41    typedef std::pair<const T*, const T*> Edge;
42    typedef std::pair<Edge, double> EdgeWeight;
43    typedef std::vector<EdgeWeight> EdgeWeights;
44  protected:
45    typedef std::vector<Edge> MaxSpanTree;
46
47    MaxSpanTree MST;
48
49  public:
50    static char ID; // Class identification, replacement for typeinfo
51
52    /// MaximumSpanningTree() - Takes a vector of weighted edges and returns a
53    /// spanning tree.
54    MaximumSpanningTree(EdgeWeights &EdgeVector) {
55
56      std::stable_sort(EdgeVector.begin(), EdgeVector.end(), EdgeWeightCompare<T>());
57
58      // Create spanning tree, Forest contains a special data structure
59      // that makes checking if two nodes are already in a common (sub-)tree
60      // fast and cheap.
61      EquivalenceClasses<const T*> Forest;
62      for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
63           EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
64        Edge e = (*EWi).first;
65
66        Forest.insert(e.first);
67        Forest.insert(e.second);
68      }
69
70      // Iterate over the sorted edges, biggest first.
71      for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
72           EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
73        Edge e = (*EWi).first;
74
75        if (Forest.findLeader(e.first) != Forest.findLeader(e.second)) {
76          Forest.unionSets(e.first, e.second);
77          // So we know now that the edge is not already in a subtree, so we push
78          // the edge to the MST.
79          MST.push_back(e);
80        }
81      }
82    }
83
84    typename MaxSpanTree::iterator begin() {
85      return MST.begin();
86    }
87
88    typename MaxSpanTree::iterator end() {
89      return MST.end();
90    }
91  };
92
93} // End llvm namespace
94
95#endif
96