124 lines
2.9 KiB
C++
124 lines
2.9 KiB
C++
/* ----------------------------------------------------------------------------
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* GTSAM Copyright 2010, Georgia Tech Research Corporation,
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* Atlanta, Georgia 30332-0415
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* All Rights Reserved
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* Authors: Frank Dellaert, et al. (see THANKS for the full author list)
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* See LICENSE for the license information
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* -------------------------------------------------------------------------- */
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/**
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* @file DSFMap.h
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* @date Oct 26, 2013
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* @author Frank Dellaert
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* @brief Allow for arbitrary type in DSF
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*/
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#pragma once
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#include <map>
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#include <set>
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#include <cstdlib> // Provides size_t
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namespace gtsam {
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/**
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* Disjoint set forest using an STL map data structure underneath
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* Uses rank compression and union by rank, iterator version
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* @addtogroup base
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*/
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template<class KEY>
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class DSFMap {
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protected:
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/// We store the forest in an STL map, but parents are done with pointers
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struct Entry {
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typename std::map<KEY, Entry>::iterator parent_;
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size_t rank_;
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Entry() {}
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};
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typedef typename std::map<KEY, Entry> Map;
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typedef typename Map::iterator iterator;
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mutable Map entries_;
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/// Given key, find iterator to initial entry
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iterator find__(const KEY& key) const {
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static const Entry empty;
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iterator it = entries_.find(key);
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// if key does not exist, create and return itself
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if (it == entries_.end()) {
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it = entries_.insert(std::make_pair(key, empty)).first;
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it->second.parent_ = it;
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it->second.rank_ = 0;
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}
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return it;
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}
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/// Given iterator to initial entry, find the root Entry
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iterator find_(const iterator& it) const {
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// follow parent pointers until we reach set representative
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iterator& parent = it->second.parent_;
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if (parent != it)
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parent = find_(parent); // not yet, recurse!
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return parent;
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}
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/// Given key, find the root Entry
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inline iterator find_(const KEY& key) const {
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iterator initial = find__(key);
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return find_(initial);
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}
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public:
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typedef std::set<KEY> Set;
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/// constructor
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DSFMap() {
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}
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/// Given key, find the representative key for the set in which it lives
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inline KEY find(const KEY& key) const {
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iterator root = find_(key);
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return root->first;
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}
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/// Merge two sets
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void merge(const KEY& x, const KEY& y) {
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// straight from http://en.wikipedia.org/wiki/Disjoint-set_data_structure
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iterator xRoot = find_(x);
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iterator yRoot = find_(y);
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if (xRoot == yRoot)
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return;
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// Merge sets
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if (xRoot->second.rank_ < yRoot->second.rank_)
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xRoot->second.parent_ = yRoot;
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else if (xRoot->second.rank_ > yRoot->second.rank_)
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yRoot->second.parent_ = xRoot;
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else {
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yRoot->second.parent_ = xRoot;
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xRoot->second.rank_ = xRoot->second.rank_ + 1;
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}
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}
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/// return all sets, i.e. a partition of all elements
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std::map<KEY, Set> sets() const {
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std::map<KEY, Set> sets;
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iterator it = entries_.begin();
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for (; it != entries_.end(); it++) {
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iterator root = find_(it);
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sets[root->first].insert(it->first);
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}
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return sets;
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}
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};
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}
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