Reverse words of a sentence - ruby

Question

I want to reverse a sentence. For example, my string is like follows.
str = "I am a good boy"
I want the result "boy good a am I". I can reverse the string by using built in Ruby methods like:
str.split(" ").reverse.join(" ") #=> "boy good a am I"
Is there any way to do this without using Ruby built in methods?

Answer 1

Sure, there is the way. In fact my favorite way. You said you don't want to use Ruby's builtins. Well, we won't. What about native extensions? I know people love them.
Firstly, create reverse/reverse.c file. Most of the source I took here.
#include "ruby/ruby.h"
void reverseWords(char *s)
{
char *word_begin = NULL;
char *temp = s;
while( *temp )
{
if (( word_begin == NULL ) && (*temp != ' ') )
{
word_begin=temp;
}
if(word_begin && ((*(temp+1) == ' ') || (*(temp+1) == '\0')))
{
reverse(word_begin, temp);
word_begin = NULL;
}
temp++;
}
reverse(s, temp-1);
}
void reverse(char *begin, char *end)
{
char temp;
while (begin < end)
{
temp = *begin;
*begin++ = *end;
*end-- = temp;
}
}
VALUE reverse_words(VALUE str)
{
char *s;
s = RSTRING_PTR(str);
reverseWords(s);
return str;
}
void Init_reverse_words()
{
VALUE string = rb_const_get(rb_cObject, rb_intern("String"));
rb_define_method(string, "reverse_words!", reverse_words, 0);
}
Secondly, create reverse/extconf.rb file:
require 'mkmf'
create_makefile('reverse_words')
Thirdly, in terminal cd to reverse folder and run:
$ ruby extconf.rb
$ make && make install
Finally, test it at irb.
irb(main):001:0> require 'reverse_words'
=> true
irb(main):002:0> "foo bar baz".reverse_words!
=> "baz bar foo"
That's the way to reverse words order without using builtins.

Answer 2

You can reverse an Array by pop ing each element into a new Array
arr, new_arr = ["I", "am", "a", "good", "boy"], []
for i in 0...arr.length do
new_arr << arr[arr.length - 1 - i]
end
new_arr
# => ["boy", "good", "a", "am", "I"]

Answer 3

TRy this
def reverse(string)
reverse = ""
index = 0
while index < string.length
reverse = string[index] + reverse
index += 1
end
return reverse
end
reverse_sent = reverse(""I am a good boy"")
reverse_sent.split.map{|word| reverse(word)}.join(" ")

Answer 4

You can not.
In ruby, you'll always end up using just an other methods, or reimplementing some that already exist (like other answer did).
In C maybe you could, using dynamic length array, but in ruby you MUST use the builtins methods.

Answer 5

Is there any way to do this without using Ruby built in methods?
No.
Ruby is an object-oriented language. In OO, you do things by calling methods. There is no other way to perform any action.
Okay, technically, there are some corners where Ruby is not object-oriented: if, &&, ||, and and or have no corresponding methods. So, that's all you can use.