110 lines
2 KiB
C
110 lines
2 KiB
C
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//
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// This source code is property of the Computer Graphics and Visualization
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// chair of the TU Dresden. Do not distribute!
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// Copyright (C) 2015-2017 CGV TU Dresden - All Rights Reserved
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//
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#pragma once
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#include <vector>
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#include <unordered_map>
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#include <random>
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/*
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Usage:
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//C++0x Random Engine Mersenne Twister
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std::mt19937 eng;
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//a set data structure with amortize constant time insertion, removal, and uniform random sampling from its elements
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sample_set<int> my_set;
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my_set.reserve(3);
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my_set.insert(1);
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my_set.insert(2);
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my_set.insert(6);
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int rand_elem1 = my_set.sample(eng);//1,2 or 6
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my_set.remove(2);
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int rand_elem2 = my_set.sample(eng); //1 or 6
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*/
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template <typename T>
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struct sample_set
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{
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typedef int element_index;
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std::vector<T> elements;
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std::unordered_map<T,element_index> index_lut;
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//create empty set
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sample_set(){}
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//reserve memory for n elements
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void reserve(size_t n)
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{
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elements.reserve(n);
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index_lut.rehash(n);
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}
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//insert element elem into set
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void insert(const T& elem)
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{
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//guard against duplicates
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if (index_lut.find(elem) == index_lut.end())
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{
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element_index idx = (element_index)elements.size();
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elements.push_back(elem);
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index_lut[elem]=idx;
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}
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}
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//remove element elem from set
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bool remove(const T& elem)
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{
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auto it = index_lut.find(elem);
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if(it == index_lut.end())
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{
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return false;
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}
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int i = it->second;
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std::swap(elements[i],elements.back());
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elements.pop_back();
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index_lut.erase(it);
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if(unsigned(i) < elements.size())
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{
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index_lut[elements[i]]=i;
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}
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return true;
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}
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//draw a sample from set
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template <typename Engine>
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const T& sample(Engine& eng)
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{
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int b = (element_index)(elements.size()-1);
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std::uniform_int_distribution<int> uniform_dist(0,b);
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element_index idx = uniform_dist(eng);
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return elements[idx];
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}
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//returns number of elements in set
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size_t size() const
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{
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return elements.size();
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}
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//returns true if set is empty
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bool empty() const
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{
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return elements.empty();
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}
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};
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