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以下都是从国外网站翻译过来，自己学习的时候总结了一下，希望对大家学习ruby有所帮助。
1. Problem: “Display series of numbers (1,2,3,4, 5….etc) in an infinite loop. The program should quit if someone hits a specific key (Say ESCAPE key).”
解决方案
1. i = 0
2. loop { print "#{i+=1}, " }
虽然是一个很简单的问题，但我想着想着却觉得这个问题很有意思，原文中也没有给出很完美的答案，不知道谁有好的解决方法。
2. Problem: “Fibonacci series, swapping two variables, finding maximum/minimum among a list of numbers.”
解决方案
1. #Fibonacci series
2. Fib = Hash.new{ |h, n| n < 2 ? h[n] = n : h[n] = h[n - 1] + h[n - 2] }
3. puts Fib[50]
4.
5. #Swapping two variables
6. x,y = y,x
7.
8. #Finding maximum/minimum among a list of numbers
9. puts [1,2,3,4,5,6].max
10. puts [7,8,9,10,11].min
语法知识：
1.Hash。Hash在实例话的时候可以在new里边接受一个参数值，或者一个模块，它实际上不是hash对象的一个值，仅当在hash操作的时候找不到这个值对应的项的时候返回。
2.交换两个变量。
3.查询数组里最大最小的值，有专门的API。
3. Problem: “Accepting series of numbers, strings from keyboard and sorting them ascending, descending order.”
解决方案
1. a = []
2. loop { break if (c = gets.chomp) == ‘q’; a << c }
3. p a.sort
4. p a.sort { |a,b| b<=>a }
语法：
1. loop循环，及break的应用
2. 从键盘读入字符 gets.chomp
3. 将一项插入到数组 a << c
4. 对于数组的正序和倒序的排序。
4. Problem: “Reynolds number is calculated using formula (D*v*rho)/mu Where D = Diameter, V= velocity, rho = density mu = viscosity Write a program that will accept all values in appropriate units (Don’t worry about unit conversion) If number is < 2100, display Laminar flow, If it’s between 2100 and 4000 display 'Transient flow' and if more than '4000', display 'Turbulent Flow' (If, else, then...)"
ruby 代码
1. vars = %w{D V Rho Mu}
2.
3. vars.each do |var|
4. print "#{var} = "
5. val = gets
6. eval("#{var}=#{val.chomp}")
7. end
8.
9. reynolds = (D*V*Rho)/Mu.to_f
10.
11. if (reynolds < 2100)
12. puts "Laminar Flow"
13. elsif (reynolds > 4000)
14. puts "Turbulent Flow"
15. else
16. puts "Transient Flow"
17. end
语法：
没有搞清楚vars = %w{D V Rho Mu} 这一句是什么意思。
5. Problem: “Modify the above program such that it will ask for ‘Do you want to calculate again (y/n), if you say ‘y’, it’ll again ask the parameters. If ‘n’, it’ll exit. (Do while loop) While running the program give value mu = 0. See what happens. Does it give ‘DIVIDE BY ZERO’ error? Does it give ‘Segmentation fault..core dump?’. How to handle this situation. Is there something built in the language itself? (Exception Handling)”
ruby 代码
1. vars = { "d" => nil, "v" => nil, "rho" => nil, "mu" => nil }
2.
3. begin
4. vars.keys.each do |var|
5. print "#{var} = "
6. val = gets
7. vars[var] = val.chomp.to_i
8. end
9.
10. reynolds = (vars["d"]*vars["v"]*vars["rho"]) / vars["mu"].to_f
11. puts reynolds
12.
13. if (reynolds < 2100)
14. puts "Laminar Flow"
15. elsif (reynolds > 4000)
16. puts "Turbulent Flow"
17. else
18. puts "Transient Flow"
19. end
20.
21. print "Do you want to calculate again (y/n)? "
22. end while gets.chomp != "n"
6.一个计算器的问题，代码太多。
7. Problem: “Printing output in different formats (say rounding up to 5 decimal places, truncating after 4 decimal places, padding zeros to the right and left, right and left justification)(Input output operations)”
ruby 代码
1. #rounding up to 5 decimal pleaces
2. puts sprintf("%.5f", 124.567896)
3.
4. #truncating after 4 decimal places
5. def truncate(number, places)
6. (number * (10 ** places)).floor / (10 ** places).to_f
7. end
8.
9. puts truncate(124.56789, 4)
10.
11. #padding zeroes to the left
12. puts ‘hello’.rjust(10,’0‘)
13.
14. #padding zeroes to the right
15. puts ‘hello’.ljust(10,’0‘)
16.
17.
语法：
1. 格式化sprintf。
2. 左填充和右填充
8. Problem: “Open a text file and convert it into HTML file. (File operations/Strings)”
这段代码比较长，其中有些东西还是不太理解，还要看看正则表达式，谁能告诉我下边的代码是怎么执行的吗：
1. rules = {‘*something*’ => ‘something’,
2. ’/something/’ => ‘something’}
3.
4. rules.each do |k,v|
5. re = Regexp.escape(k).sub(/something/) {"(.+?)"}
6. doc.gsub!(Regexp.new(re)) do
7. content = $1
8. v.sub(/something/) { content }
9. end
10. end
9. Problem: “Time and Date : Get system time and convert it in different formats ‘DD-MON-YYYY’, ‘mm-dd-yyyy’, ‘dd/mm/yy’ etc.”
ruby 代码
1. time = Time.now
2. puts time.strftime("%d-%b-%Y")
3. puts time.strftime("%m-%d-%Y")
4. puts time.strftime("%d/%m/%Y")
10. Problem: “Create files with date and time stamp appended to the name”
ruby 代码
1. #Create files with date and time stamp appended to the name
2. require 'date'
3.
4. def file_with_timestamp(name)
5. t = Time.now
6. open("#{name}-#{t.strftime('%m.%d')}-#{t.strftime('%H.%M')}", 'w')
7. end
8.
9. my_file = file_with_timestamp('pp.txt')
10. my_file.write('This is a test!')
11. my_file.close
11. Problem: “Input is HTML table. Remove all tags and put data in a comma/tab separated file.”
12. Problem: “Extract uppercase words from a file, extract unique words.”
1. open('some_uppercase_words.txt').read.split().each { |word| puts word if word =~ /^[A-Z]+$/ }
2.
3. words = open(some_repeating_words.txt).read.split()
4. histogram = words.inject(Hash.new(0)) { |hash, x| hash[x] += 1; hash}
5. histogram.each { |k,v| puts k if v == 1 }
语法：（对于第四行还是不太懂，谁能给我讲一下呢）
1.打开文件，读取文件，split（），正则表达式匹配。
13. Problem: “Implement word wrapping feature (Observe how word wrap works in windows ‘notepad’).”
ruby 代码
1. input = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
2.
3.
4. def wrap(s, len)
5. result = ''
6. line_length = 0
7. s.split.each do |word|
8. if line_length + word.length + 1 < len
9. line_length += word.length + 1
10. result += (word + ' ')
11. else
12. result += "\n"
13. line_length = 0
14. end
15. end
16. result
17. end
18.
19. puts wrap(input, 30)
14. Problem: “Adding/removing items in the beginning, middle and end of the array.”
ruby 代码
1. x = [1,3]
2.
3. #adding to beginning
4. x.unshift(0)
5. print x
6. print "\n"
7.
8. #adding to the end
9. x << 4
10. print x
11. print "\n"
12. #adding to the middle
13. x.insert(2,2)
14. print x
15. print "\n"
16. #removing from the beginning
17. x.shift
18. print x
19. print "\n"
20. #removing from the end
21. x.pop
22. print x
23. print "\n"
24. #removing from the middle
25. x.delete(2)
26. print x
27. print "\n
15. Problem: “Are these features supported by your language: Operator overloading, virtual functions, references, pointers etc.”
Solution: Well this is not a real problem (not in Ruby, at least). Ruby is a very high level language ant these things are a must  . |
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发表于 2009-8-20 17:06:06
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