Submission #3013010

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Source Code Expand

class UnionFind
  attr_reader :rank, :parent, :value
  attr_writer :rank, :parent

  def initialize(x)
    @value = x
    @rank = 0
    @parent = self
  end

  def ==(obj)
    @value == obj.value
  end

  def find
    return self if self.parent == self
    root = self.parent.find
    self.parent = root
    root
  end

  def union(y)
    xr = find; yr = y.find
    return if xr == yr
    if xr.rank >= yr.rank
      yr.parent = xr
      xr.rank += 1
    else
      y.union(self)
    end
  end
end

def minimum_spanning_tree_kruskal(nodes, edges)
  # edges: [[node_from, node_to, weight]]
  edges.sort_by!{ |e| e[2] }
  th = Hash[nodes.map{ |x| [x, UnionFind.new(x)] }]
  i = 0
  mst = []
  while i < edges.size
    e = edges[i]
    i += 1
    f,t,w = *e
    tf = th[f]; tt = th[t]
    next if (tf.find == tt.find)
    tf.union(tt)
    mst << e
  end
  mst
end

N = gets.to_i
ns = (0...N).map{ |i| x,y = gets.split.map(&:to_i); { i: i, x: x, y: y } }
es = {}

[ :x, :y ].each{ |s|
  ns.sort_by!{ |n| n[s] }
  (1...N).each{ |i| 
    f,t = ns[i-1][:i],ns[i][:i]
    es[f] ||= {}
    es[f][t] = [ns[i][:x] - ns[i-1][:x], ns[i][:y] - ns[i-1][:y]].map(&:abs).min
  }
}

p minimum_spanning_tree_kruskal((0...N).to_a, es.map{ |f,e| e.map{ |t,w| [f,t,w] } }.flatten(1)).map{ |e| e[2] }.inject(:+)

Submission Info

Compile Error

./Main.rb:43: warning: assigned but unused variable - w

Judge Result