减法算式20以内

DEC_X_RANGE = (10..20)		#第一个减数的范围
DEC_Y_RANGE = (1..20)		#第二个减数的范围
LINE_CNTS = 5				#每行算式个数
DEC_FORMULA_CNTS = 100		#算式总的个数

res = {}
while res.size < DEC_FORMULA_CNTS do
	x =  rand(DEC_X_RANGE)
	y =  rand(DEC_Y_RANGE)
	if (x-y) > 0
		key = sprintf("%d-%d", x, y)
		str = sprintf("%-2d - %-2d =     ", x, y)
		res[key] = str
	end 
end


line  = 0
res.each{|x,y|
	printf(y)
	line = line + 1
	if line == LINE_CNTS
		puts ""
		puts ""

		line = 0
	end
}