cppvisgraph/src/cppvisgraph/shortest_path.hpp at master · emranemon/cppvisgraph · GitHub

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// The MIT License (MIT)

// https://github.com/emranemon

// Permission is hereby granted, free of charge, to any person obtaining a copy

// of this software and associated documentation files (the "Software"), to deal

// in the Software without restriction, including without limitation the rights

// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

// copies of the Software, and to permit persons to whom the Software is

// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all

// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

// SOFTWARE.

#ifndef CPPVISGRAPH_SHORTEST_PATH_HPP

#define CPPVISGRAPH_SHORTEST_PATH_HPP

#include "graph.hpp"

#include "visible_vertices.hpp"

#include <unordered_map>

#include <vector>

#include <algorithm>

#include <functional>

#include <utility>

#include <queue>

#include <string>

namespace cppvisgraph

{

/**

* @brief Hashmap that can be used as a priority queue.

* This is a replica of priority_dict(dict) implemented in python

* Keys of the hashmap are items to be put into the queue, and values

* are their respective priorities. All hashmap methods work as expected.

* The advantage over a standard heapq-based priority queue is that priorities

* of items can be efficiently updated (amortized O(1)) using code as

* 'themap.push(item, new_priority).'

* Note that this is a modified version of

* https://gist.github.com/matteodellamico/4451520

template <typename Key, typename Value, typename Hash = std::hash<Key>>

class priority_dict : public std::unordered_map<Key, Value, Hash>

{

private:

typedef std::pair<Value, Key> ValueKeyPair;

struct Greater

{

bool operator()(const ValueKeyPair& lhs, const ValueKeyPair& rhs)

{

return lhs.first > rhs.first; // Greater than for min-heap, Smaller than for max-heap

}

};

std::priority_queue<ValueKeyPair, std::vector<ValueKeyPair>, Greater> stl_heap;

public:

void push(Key key, Value value)

{

auto result = this->emplace(key, value);

if(!result.second)

{

result.first->second = value;

}

stl_heap.push(std::make_pair(value, key));

}

std::pair<Key, Value> pop()

{

auto vk = stl_heap.top();

auto v = vk.first;

auto k = vk.second;

stl_heap.pop();

while (this->count(k)==0 || this->at(k) != v)

{

vk = stl_heap.top();

v = vk.first;

k = vk.second;

stl_heap.pop();

}

this->erase(k);

return std::pair<Key, Value>(k, v);

}

}; // class priority_dict

class ShortestPath

{

private:

static std::pair<std::unordered_map<Point, double, PointHash>, std::unordered_map<Point, Point, PointHash>> dijkstra(

const Graph& graph, const Point& origin, const Point& destination, const Graph& add_to_visgraph)

{

std::unordered_map<Point, double, PointHash> D;

std::unordered_map<Point, Point, PointHash> P;

priority_dict<Point, double, PointHash> Q;

Q.push(origin, 0);

while (!Q.empty())

{

auto top = Q.pop();

Point v = top.first;

D[v] = top.second;

if (v == destination) break;

std::unordered_set<Edge, EdgeHash> edges = graph[v];

if (add_to_visgraph.contains(v) && !add_to_visgraph[v].empty())

{

edges.insert(add_to_visgraph[v].begin(), add_to_visgraph[v].end());

}

for (const Edge& e : edges)

{

Point w = e.get_adjacent(v);

double elength = D.at(v) + PolygonUtils::edge_distance(v, w);

if (D.find(w) != D.end())

{

if (elength < D.at(w))

{

throw std::runtime_error("Shorter path found, contradicting the assumption of shortest distances.");

}

else if (Q.find(w) == Q.end() || elength < Q.at(w))

{

Q.push(w, elength);

auto p = P.emplace(w, v);

if (!p.second) { p.first->second = v; }

}

return std::make_pair(D, P);

}

public:

static std::vector<Point> get(const Graph& graph, const Point& origin, const Point& destination,

const Graph& add_to_visgraph = Graph())

{

auto dp = ShortestPath::dijkstra(graph, origin, destination, add_to_visgraph);

std::unordered_map<Point, double, PointHash> D = dp.first;

std::unordered_map<Point, Point, PointHash> P = dp.second;

std::vector<Point> path;

Point back_to_origin = destination;

while (true)

{

path.push_back(back_to_origin);

if (back_to_origin == origin) break;

back_to_origin = P.at(back_to_origin);

}

std::reverse(path.begin(), path.end());

return path;

}

}; // class ShortestPath

} // namespace cppvisgraph

#endif //CPPVISGRAPH_SHORTEST_PATH_HPP

cppvisgraph/src/cppvisgraph/shortest_path.hpp at master · emranemon/cppvisgraph · GitHub

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