airport-distances.rb

#!/usr/bin/ruby

require './dijkstra'

def haversine (lat1, lon1, lat2, lon2)
    r = 6371 # earth radius, km
    degToRadConvFac = Math::PI / 180
    
    p1 = lat1 * degToRadConvFac
    p2 = lat2 * degToRadConvFac
    delP = (lat2 - lat1) * degToRadConvFac
    delL = (lon2 - lon1) * degToRadConvFac
    
    a = Math.sin(delP/2) * Math.sin(delP/2) + Math.cos(p1) * Math.cos(p2) * Math.sin(delL/2) * Math.sin(delL/2)
    
    c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))
    d = r * c
end

# Open airports.dat
# On each line, airport IATA code = 5th value, latitude = 7th value, longitude = 8th value
# Populate airport IATA code, latitude, longitude in a data structure (hash, key=code, value=list[latitude, longitude])
h = Hash.new {|hash, key| hash[key] = []}
File.open("airports.dat", "r") do |file|
    file.each_line do |line|
        fields = line.split(/,/)
        if fields[4] != '""'
            h[fields[4].delete('"')] << fields[6] << fields[7]
        end
    end
end

# Initialize a graph
graph = Graph.new

# Open routes.dat
# On each line, orig airport IATA code = 3rd value, dest airport IATA code = 5th value
# Make Graph vertices from the IATA codes (if they are already not vertices)
# Calculate distance
# -- Get orig airport latitude & longitude, dest airport latitude & longitude
# -- and pass them to haversine method to get distance
# Connect the airports with distance as graph Edges
File.open("routes.dat", "r") do |file|
    file.each_line do |line|
        fields = line.split(/,/)
        orig = fields[2]
        dest = fields[4]
        if h.has_key?orig and h.has_key?dest
            graph.push orig if ! (graph.include?orig)
            graph.push dest if ! (graph.include?dest)

            dist = haversine h[orig][0].to_f, h[orig][1].to_f, h[dest][0].to_f, h[dest][1].to_f
            graph.connect orig, dest, dist.to_i if dist > 0
        end
    end
end

# Take an airports pair as user input
# Print the shortest path and distance
p "Enter from-city"
a = STDIN.gets.chomp
p "Enter to-city"
b = STDIN.gets.chomp
p graph.dijkstra(a, b)