69 lines
1.9 KiB
C++
69 lines
1.9 KiB
C++
#include "graph_distances.hpp"
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#include <queue>
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auto graph_distances::clear() -> void
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{
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distances.clear();
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parents.clear();
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nearest_targets.clear();
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}
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auto graph_distances::empty() const -> bool
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{
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return distances.empty() || parents.empty() || nearest_targets.empty();
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}
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auto graph_distances::calculate_distances(const size_t node_count,
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const std::vector<std::pair<size_t, size_t>>& edges,
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const std::vector<size_t>& targets) -> void
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{
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// Build a list of adjacent nodes to speed up BFS
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std::vector<std::vector<size_t>> adjacency(node_count);
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for (const auto& [from, to] : edges) {
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adjacency[from].push_back(to);
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adjacency[to].push_back(from);
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}
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distances = std::vector<int>(node_count, -1);
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parents = std::vector<size_t>(node_count, -1);
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nearest_targets = std::vector<size_t>(node_count, -1);
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std::queue<size_t> queue;
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for (size_t target : targets) {
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distances[target] = 0;
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nearest_targets[target] = target;
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queue.push(target);
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}
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while (!queue.empty()) {
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const size_t current = queue.front();
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queue.pop();
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for (size_t neighbor : adjacency[current]) {
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if (distances[neighbor] == -1) {
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// If distance is -1 we haven't visited the node yet
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distances[neighbor] = distances[current] + 1;
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parents[neighbor] = current;
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nearest_targets[neighbor] = nearest_targets[current];
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queue.push(neighbor);
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}
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}
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}
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}
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auto graph_distances::get_shortest_path(const size_t source) const -> std::vector<size_t>
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{
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if (empty() || distances[source] == -1) {
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// Unreachable
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return {};
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}
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std::vector<size_t> path;
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for (size_t n = source; n != static_cast<size_t>(-1); n = parents[n]) {
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path.push_back(n);
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}
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return path;
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} |