Re: Algorithm/code to compare values in an array

From	DFS <nospam@dfs.com>
Newsgroups	comp.lang.c
Subject	Re: Algorithm/code to compare values in an array
Date	2017-06-15 19:21 -0400
Organization	A noiseless patient Spider
Message-ID	<ohv4gu$cf9$3@dont-email.me> (permalink)
References	<ohu82o$qph$4@dont-email.me> <9fk5kc1lta08klikjmpeenhl9u9ouvrpbh@4ax.com>

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On 6/15/2017 2:43 PM, Barry Schwarz wrote:
> On Thu, 15 Jun 2017 11:16:31 -0400, DFS <nospam@dfs.com> wrote:
> 
>> Given two int arrays:
>>
>> q = {100,200};
>> s = {50,125,150,175,190,210};
>>
>> I want to find:
>>
>> 1. the min s > the min q
>> 2. the max s < the max q
>>
>> Those would be 125 and 190
> 
> Using qmin when no s[i] satisfies the condition is misleading.  
> It forces the user to check the "returned" value against qmin to identify
> the "no match" condition.

Since a range of s values may or may not be contained within q, that's 
the only way it could work.  As far as I can tell.

> Are the arrays guaranteed to be sorted?

Yes.

>> This code works fine, but maybe there's a better or shorter approach
>> than 2 loops (one forward and one backward)?
> 
> Returning the wrong answer is a strange definition of "works fine".

125 and 190 is the right answer for that set of values.

>> ------------------------------------------------
>> int main(int argc, char *argv[])
>> {
>> 	int q[] = {100,200};
>> 	int s[] = {50,125,150,175,190,210};
>>
>> 	int qmin = q[0];
>> 	int qmax = q[1];
> 
> Is q always an array of 2?

No.  But it's always evenly divisible by 2, and 2 values always form the 
upper and lower boundaries.

FYI:

I'm counting the number of words enclosed in single-quotes, enclosed in 
dbl-quotes.

q = position of dbl-quotes in the input
s = position of sgl-quotes in the input

>> 	int min_s = qmin;
>> 	int max_s = qmax;
>>
>> 	for(int i = 0; i < 5; i++)
> 
> How do you know the size of s?

The size of s is set at compile time to a relatively large value that I 
know won't be exceeded.

As s is populated I keep track of the nbr of entries, which is /not/ 
always evenly divisible by 2.

>> 	{
>> 	   if (s[i] > qmin) {min_s = s[i]; break;}
>> 	}
> 
> The code produces the wrong answer if s contains
> {50, 51, 52, 57, 59, 210}.

>> 	for(int i = 4; i >= 0; i--)
>> 	{
>> 	   if (s[i] < qmax) {max_s = s[i]; break;}
>> 	}
> 
> Same issue when q contains {100, 400}.	
> 
>> 	printf("min %d, max %d\n", min_s, max_s);	
>> 	return 0;
>> }

The code always checks the return values:

if (q[i] < min_s < max_s < q[i+1])

before moving on.

I guess I could do that check in the function and return a success or 
fail flag.  Either way.

Thread

Algorithm/code to compare values in an array DFS <nospam@dfs.com> - 2017-06-15 11:16 -0400
  Re: Algorithm/code to compare values in an array Richard Heathfield <rjh@cpax.org.uk> - 2017-06-15 16:41 +0100
    Re: Algorithm/code to compare values in an array DFS <nospam@dfs.com> - 2017-06-15 13:48 -0400
      Re: Algorithm/code to compare values in an array Richard Heathfield <rjh@cpax.org.uk> - 2017-06-15 19:47 +0100
        Re: Algorithm/code to compare values in an array Gareth Owen <gwowen@gmail.com> - 2017-06-15 20:17 +0100
          Re: Algorithm/code to compare values in an array Richard Heathfield <rjh@cpax.org.uk> - 2017-06-15 20:51 +0100
  Re: Algorithm/code to compare values in an array Barry Schwarz <schwarzb@dqel.com> - 2017-06-15 11:43 -0700
    Re: Algorithm/code to compare values in an array DFS <nospam@dfs.com> - 2017-06-15 19:21 -0400
      Re: Algorithm/code to compare values in an array Barry Schwarz <schwarzb@dqel.com> - 2017-06-15 18:49 -0700
  Re: Algorithm/code to compare values in an array Real Troll <Real.Troll@Trolls.com> - 2017-06-15 16:35 -0400
    Re: Algorithm/code to compare values in an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-15 21:34 +0100
      Re: Algorithm/code to compare values in an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-15 23:23 +0100
        Re: Algorithm/code to compare values in an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-16 00:35 +0100
          Re: Algorithm/code to compare values in an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-16 01:04 +0100
          Re: Algorithm/code to compare values in an array Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-16 01:10 +0100
        Re: Algorithm/code to compare values in an array DFS <nospam@dfs.com> - 2017-06-15 20:45 -0400
    Re: Algorithm/code to compare values in an array DFS <nospam@dfs.com> - 2017-06-15 20:00 -0400

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