Two sum: Difference between revisions

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(→‎version 2: updated the REXX program to handle the latest task requirements/specifications, used a template for the output, added a solution count (and message), added an aligned summation, indicated that solution contains (zero based) indices.)
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===version 2===
===version 2===
All solutions are listed (if any),   along with a count of the number of solutions.
This REXX version uses optimization in using integers that take advantage
that the numbers are an ordered list of positive integers.


Also, it's mentioned that the indices are zero─based,   and formatted solutions are shown.
All solutions are listed (if any).
⚫
<lang rexx>/*REXX program finds two numbers in a list of numbers that sum to a particular target.*/
parse arg targ list /*obtain optional arguments from the CL*/
if targ='' | targ="," then targ= 21 /*Not specified? Then use the defaults*/
⚫
if list='' | list="," then list= 0 2 11 19 90 /* " " " " " " */
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say 'the list: ' list /*echo the list to the terminal*/
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say 'the target sum: ' targ /* " " target sum " " " */
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sol=0; w=0 /*number of solutions found (so far). */
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do #=0 for words(list); _=word(list, #+1) /*examine the list, construct an array.*/
@.#=_; w=max(w, length(_) ) /*assign a number to an indexed array. */
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end /*#*/ /*W: the maximum width of any number. */
say /* [↓] look for sum of 2 numbers=target*/
do a=0 for # /*scan up to the last number in array. */
⚫
do b=a+1 to #-1; if @.a + @.b\=targ then iterate /*is sum not correct? */
sol=sol+1 /*bump count of the number of solutions*/
say 'a solution: zero─based indices ['a"," b']' ,
' ' right(@.a, w) " + " right(@.b, w) ' = ' targ
end /*b*/ /*show the 2 indices and the summation.*/
⚫
end /*a*/
say
if sol==0 then sols= 'None' /*prettify the number of solutions if 0*/
say 'number of solutions found: ' sol /*stick a fork in it, we're all done. */</lang>
{{out|output|text=&nbsp; when using the default inputs:}}
<pre>
the list: 0 2 11 19 90
the target sum: 21


a solution: zero─based indices [1, 3] 2 + 19 = 21
This REXX solution makes allowances for the inclusion of zero, even though it is specifically excluded by the task's description. &nbsp; However zero is included in the task's requirement.


number of solutions found: 1
If the list <u>isn't</u> an ordered list of positive integers, then
</pre>
the &nbsp; '''while''' &nbsp; clause (below) should be removed, &nbsp; and then this REXX
{{out|output|text=&nbsp; when using the input of: &nbsp; &nbsp; 21 &nbsp; &nbsp; -78 -5 -4 -1 0 1 2 3 5 11 14 16 17 18 18 19 23 24 25 26 99}}
version will work with any list &nbsp; (including negative numbers and also with any
real number.
⚫
<lang rexx>/*REXX pgm find 2 integers in a ordered list of positive integers that sum to a number. */
⚫
list=0 2 11 19 90 ; say 'order list: ' list " (using a zero index.)"
sum=21 ; say 'target sum: ' sum

⚫
do #=0 for words(list) while word(list, #+1)<=sum /*only use possibles.*/
@.#=word(list, #+1)
⚫
end /*#*/
⚫
say /* [↓] look for sum of 2 int = the sum*/
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do a=0 for # /*scan up to the last possible integer.*/
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do b=a+1 to #-1; if @.a+@.b=sum then say 'a solution: ['a"," b']'
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end /*y*/ /* [↑] 2 elements sum to target? Tell*/
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end /*x*/ /*stick a fork in it, we're all done. */</lang>
'''output'''
<pre>
<pre>
order list: 0 2 11 19 90 (using a zero index.)
the list: -78 -5 -4 -1 0 1 2 3 5 11 14 16 17 18 18 19 23 24 25 26 99
target sum: 21
the target sum: 21

a solution: zero─based indices [0, 20] -78 + 99 = 21
a solution: zero─based indices [1, 19] -5 + 26 = 21
a solution: zero─based indices [2, 18] -4 + 25 = 21
a solution: zero─based indices [6, 15] 2 + 19 = 21
a solution: zero─based indices [7, 13] 3 + 18 = 21
a solution: zero─based indices [7, 14] 3 + 18 = 21
a solution: zero─based indices [8, 11] 5 + 16 = 21


number of solutions found: 7
a solution: [1, 3]
</pre>
</pre>


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