Submission #32150851

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Source Code Expand

N,K = gets.split.map(&:to_i)
exit~p(-1) if (N-1)*(N-2)/2<K

E = Array.new(N+1){[]}
T = (0..).find{|t| K<=t*(t+1)/2+N-2-t }
Over = T*(T+1)/2+N-2-T-K
#warn [N,K,T,Over].inspect
(2..2+T).each{|v|
	E[1]<<v
}
if 0<T
	Over.times{|t|
		E[T+2]<<T+1-t
	}
	[2,*3+T..N].each_cons(2){|u,v|
		E[u]<<v
	}
else
	(3..N-Over).each{|v|
		E[v].concat [*1...v]-[v-2]
	}
	Over.times{|t|
		E[N-t].concat [*1...N-t]
	}
end
#warn E.inspect

p E.sum(&:size)
E.each_with_index{|bs,a|
	puts bs.map{|b| "#{a} #{b}" }
}

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