Graph/DiameterPath.cpp

• View this file on GitHub
• Last update: 2021-03-22 17:28:05+09:00

Depends on

• Graph/GraphTemplate.cpp

Verified with

• test/Diameter.test.cpp

Code

#pragma once
#include "./GraphTemplate.cpp"
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <functional>

std::tuple<Weight, std::vector<int>> DiameterPath(const Graph& graph) {
	int n = graph.size();
	std::vector<Weight> dist0(n);
	auto dfs = [&](auto self, int v, int p, Weight d) -> void {
		dist0[v] = d;
		for (const auto& u : graph[v])
			if (u.to != p) {
				self(self, u.to, v, d + u.cost);
			}
	};
	dfs(dfs, 0, -1, 0);

	int s = std::max_element(dist0.begin(), dist0.end()) - dist0.begin();
	std::vector<Weight> dist(n);
	std::vector<int> par(n);
	auto dfs2 = [&](auto self, int v, int p, Weight d) -> void {
		dist[v] = d;
		par[v] = p;
		for (const auto& u : graph[v]) {
			if (u.to != p) {
				self(self, u.to, v, d + u.cost);
			}
		}
	};
	dfs2(dfs2, s, -1, 0);
	auto t = std::max_element(dist.begin(), dist.end());
	std::vector<int> path{static_cast<int>(t - dist.begin())};
	for (int p = 0; (p = par[path.back()]) != -1;) {
		path.push_back(p);
	}
	std::reverse(path.begin(), path.end());
	return {*t, path};
}

#line 2 "Graph/GraphTemplate.cpp"
#include <vector>
#include <utility>
#include <iostream>
#include <limits>

using Weight = long long;
constexpr Weight INF = std::numeric_limits<Weight>::max();
struct Edge {
	int to;
	Weight cost;
	Edge() : to(-1), cost(-1) {}
	Edge(int _to, Weight _cost = 1) : to(_to), cost(_cost) {}
	friend bool operator<(const Edge& e1, const Edge& e2) {
		return e1.cost < e2.cost;
	}
	friend bool operator>(const Edge& e1, const Edge& e2) {
		return e1.cost > e2.cost;
	}
	friend std::ostream& operator<<(std::ostream& os, const Edge& e) {
		return os << "->" << e.to << '(' << e.cost << ')';
	}
};
using UnWeightedGraph = std::vector<std::vector<int>>;
using Graph = std::vector<std::vector<Edge>>;
struct Edge2 {
	int from, to;
	Weight cost;
	Edge2() : from(-1), to(-1), cost(0) {}
	Edge2(int _from, int _to, Weight _cost) : from(_from), to(_to), cost(_cost) {}
	friend bool operator<(const Edge2& e1, const Edge2& e2) {
		return e1.cost < e2.cost;
	}
	friend bool operator>(const Edge2& e1, const Edge2& e2) {
		return e1.cost > e2.cost;
	}
	friend std::ostream& operator<<(std::ostream& os, const Edge2& e) {
		return os << e.from << "->" << e.to << '(' << e.cost << ')';
	}
};
using UnWeightedEdges = std::vector<std::pair<int, int>>;
using Edges = std::vector<Edge2>;
using Matrix = std::vector<std::vector<Weight>>;

auto add_edge(UnWeightedGraph& graph, int v, int u) {
	graph[v].push_back(u);
	graph[u].push_back(v);
}
auto add_edge(Graph& graph, int v, int u, Weight cost) {
	graph[v].emplace_back(u, cost);
	graph[u].emplace_back(v, cost);
}
auto to_graph(const UnWeightedGraph& graph, Weight cost = 1) {
	Graph result(graph.size());
	for (std::size_t i = 0; i < graph.size(); ++i) {
		for (int v : graph[i]) {
			result[i].emplace_back(v, cost);
		}
	}
	return result;
}
auto to_unweighted_graph(const Graph& graph) {
	UnWeightedGraph result(graph.size());
	for (std::size_t i = 0; i < graph.size(); ++i) {
		for (auto [v, cost] : graph[i]) {
			result[i].push_back(v);
		}
	}
	return result;
}
auto to_edges(const UnWeightedGraph& graph, bool unique = false) {
	std::vector<std::pair<int, int>> edges;
	for (std::size_t i = 0; i < graph.size(); ++i) {
		for (int v : graph[i]) {
			if (!unique || static_cast<int>(i) < v) edges.emplace_back(i, v);
		}
	}
	return edges;
}
auto to_edges(const Graph& graph) {
	Edges edges;
	for (std::size_t i = 0; i < graph.size(); ++i) {
		for (auto [v, cost] : graph[i]) {
			edges.emplace_back(i, v, cost);
		}
	}
	return edges;
}
#line 4 "Graph/DiameterPath.cpp"
#include <algorithm>
#line 6 "Graph/DiameterPath.cpp"
#include <tuple>
#include <functional>

std::tuple<Weight, std::vector<int>> DiameterPath(const Graph& graph) {
	int n = graph.size();
	std::vector<Weight> dist0(n);
	auto dfs = [&](auto self, int v, int p, Weight d) -> void {
		dist0[v] = d;
		for (const auto& u : graph[v])
			if (u.to != p) {
				self(self, u.to, v, d + u.cost);
			}
	};
	dfs(dfs, 0, -1, 0);

	int s = std::max_element(dist0.begin(), dist0.end()) - dist0.begin();
	std::vector<Weight> dist(n);
	std::vector<int> par(n);
	auto dfs2 = [&](auto self, int v, int p, Weight d) -> void {
		dist[v] = d;
		par[v] = p;
		for (const auto& u : graph[v]) {
			if (u.to != p) {
				self(self, u.to, v, d + u.cost);
			}
		}
	};
	dfs2(dfs2, s, -1, 0);
	auto t = std::max_element(dist.begin(), dist.end());
	std::vector<int> path{static_cast<int>(t - dist.begin())};
	for (int p = 0; (p = par[path.back()]) != -1;) {
		path.push_back(p);
	}
	std::reverse(path.begin(), path.end());
	return {*t, path};
}

Back to top page