Peña, Botp
1/16/2007 2:17:00 AM
From: Cyrus Gabilla [mailto:gabilla19992004@yahoo.com] :
#---------------------------------------------------------------
# I am trying to solve these three problems in Ruby. I do not
# know if my solutions are really correct. I just wanted to ask
#---------------------------------------------------------------
test it :)
#---------------------------------------------------------------
# 1. Write a one-line in irb using Range#inject to calculate
# 20!. Generalize this into a function.
#---------------------------------------------------------------
fri is your friend
C:\Documents and Settings\peñaijm>fri inject
c:0:Warning: require_gem is obsolete. Use gem instead.
------------------------------------------------------ Enumerable#inject
enum.inject(initial) {| memo, obj | block } => obj
enum.inject {| memo, obj | block } => obj
------------------------------------------------------------------------
Combines the elements of _enum_ by applying the block to an
accumulator value (_memo_) and each element in turn. At each step,
_memo_ is set to the value returned by the block. The first form
lets you supply an initial value for _memo_. The second form uses
the first element of the collection as a the initial value (and
skips that element while iterating).
# Sum some numbers
(5..10).inject {|sum, n| sum + n } #=> 45
# Multiply some numbers
(5..10).inject(1) {|product, n| product * n } #=> 151200
# find the longest word
longest = %w{ cat sheep bear }.inject do |memo,word|
memo.length > word.length ? memo : word
end
longest #=> "sheep"
# find the length of the longest word
longest = %w{ cat sheep bear }.inject(0) do |memo,word|
memo >= word.length ? memo : word.length
end
longest #=> 5
#---------------------------------------------------------------
# 2. Write a function to find the longest string in an array
# of strings.
#---------------------------------------------------------------
fri is your friend
C:\Documents and Settings\peñaijm>fri max
c:0:Warning: require_gem is obsolete. Use gem instead.
------------------------------------------------------ Multiple choices:
Enumerable#max, SizedQueue#max
C:\Documents and Settings\peñaijm>fri enumerable#max
c:0:Warning: require_gem is obsolete. Use gem instead.
--------------------------------------------------------- Enumerable#max
enum.max => obj
enum.max {|a,b| block } => obj
------------------------------------------------------------------------
Returns the object in _enum_ with the maximum value. The first form
assumes all objects implement +Comparable+; the second uses the
block to return _a <=> b_.
a = %w(albatross dog horse)
a.max #=> "horse"
a.max {|a,b| a.length <=> b.length } #=> "albatross"
C:\Documents and Settings\peñaijm>
#---------------------------------------------------------------
# 3. Write an iterator function n_times(n) that calls the
# given block n times.
#---------------------------------------------------------------
again, fri is your friend
C:\Documents and Settings\peñaijm>fri integer#times
c:0:Warning: require_gem is obsolete. Use gem instead.
---------------------------------------------------------- Integer#times
int.times {|i| block } => int
------------------------------------------------------------------------
Iterates block _int_ times, passing in values from zero to _int_ -
1.
5.times do |i|
print i, " "
end
_produces:_
0 1 2 3 4
C:\Documents and Settings\peñaijm>fri iterator
c:0:Warning: require_gem is obsolete. Use gem instead.
------------------------------------------------------- Kernel#iterator?
block_given? => true or false
iterator? => true or false
------------------------------------------------------------------------
Returns +true+ if +yield+ would execute a block in the current
context. The +iterator?+ form is mildly deprecated.
def try
if block_given?
yield
else
"no block"
end
end
try #=> "no block"
try { "hello" } #=> "hello"
try do "hello" end #=> "hello"
hth.
kind regards -botp