How do I optimize* this?

Question

My code extract is

if (num == 0) {
    cout << 1;
    cout << 2;
}
else if (num == 1) {
    cout << 0;
    cout << 2;
}
else if (num == 2) {
    cout << 0;
    cout << 1;
}

where 0 <= num <= 2.

I am asking because the cout << ... statements will be converted into something much larger, but (almost) identical to each other.

*I mean optimize as 'beautify' the code (ex. remove the 5 repeated cout statements).

^{^{I didn't put "beautify" in the question because it just sounds weird in a SO question.}}

Use a table per value. Feed the table per value into cout. This is less about optimization and more about reducing redundant code and making things easier to maintain. — Michael Dorgan, Nov 11 '17 at 01:06
Why would `cout << ...` be *converted into something much larger*? They're just [function calls](http://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt). — Praetorian, Nov 11 '17 at 01:07
Well the last `else if` can just be an `else` if you don't have to worry about anything else. — NathanOliver, Nov 11 '17 at 01:09
@DimChtz I meant optimize as 'beautify and/or remove repeated code (like the 5 repetitions of cout'. But any of those phrases would be weird in the question. — sudomeacat, Nov 11 '17 at 01:22
@sudomeacat: please put the information you gave to DimChtz in the comments (what you mean by optimize), and I'll upvote your question then, because it is clearly not a bad question. — geza, Nov 11 '17 at 02:01
@geza I'm sure this is the comments, but did you mean the question (just making sure)? — sudomeacat, Nov 11 '17 at 02:10
Yes, I was ambiguous. I meant to please edit your question, and put the information what you gave to DimChtz. — geza, Nov 11 '17 at 02:21
For future reference, questions like this don't belong on StackOverflow. If the code works in general, and you just want to clean it up and make it better, ask on [CodeReview](http://codereview.stackexchange.com) instead. — Remy Lebeau, Nov 11 '17 at 03:36

score 6 · Answer 1 · answered Nov 11 '17 at 01:23

6

Perhaps this?

cout << "100"[num];
cout << "221"[num];

answered Nov 11 '17 at 01:23

geza

28,403
6
61
135

That is cute. Why use 1 table lookup, when you can have 2 with 0 compares. Nice solution. – Michael Dorgan Nov 11 '17 at 01:26
@MichaelDorgan: if you like it, then check out this :) https://stackoverflow.com/a/45249531/8157187 – geza Nov 11 '17 at 01:30
@MichaelDorgan: woha, I didn't know that this kind of stuff actually has a name. Code golf, cool :) – geza Nov 11 '17 at 01:34
That's a really creative answer, but wouldn't the result of string::operator[] be a char? (I mean I guess I could subtract '0' from it.) But it would be fun to see this in code golf. – sudomeacat Nov 11 '17 at 01:53
@sudomeacat: it prints it as a char (you cannot differentiate between '1' and 1, when it's printed). If you do need an integer, then yes, your subtraction idea works. Or, you could get dirty, and use `"\x01\x00\x00"[num]` :) But maybe a proper `static const char table[2][3] = { ... };` is a better idea. – geza Nov 11 '17 at 01:56

score 2 · Accepted Answer · answered Nov 11 '17 at 01:02

2

Something along these lines, perhaps:

for (int i : {0, 1, 2}) {  // or for (int i = 0; i <= 2; ++i) {
  if (i != num) {
    std::cout << i;
  }
}

answered Nov 11 '17 at 01:02

Igor Tandetnik

50,461
4
56
85

Lol - but this still has 3 compares! How can that be faster than... waiting for an eternity for cout to run. – Michael Dorgan Nov 11 '17 at 01:08
2

@MichaelDorgan I understood "optimize" to mean not so much "make this code faster" but rather "organize this code better". To reduce repetition. – Igor Tandetnik Nov 11 '17 at 01:09
And I completely agree, otherwise this is a fruitless adventure with no real prize to be had. My comment was complete sarcasm. Forgot the markups. – Michael Dorgan Nov 11 '17 at 01:11

DimChtz · Answer 3 · 2017-11-11T01:33:52.770

1

Well, here's something different (without if or for):

cout << ( (n + 1) % 2); 
cout << ( (n + 2) % 2) + (2 - n);

Obviously: n = 0,1,2.

edited Nov 11 '17 at 01:33

answered Nov 11 '17 at 01:28

DimChtz

4,043
2
21
39

score 0 · Answer 4 · answered Nov 11 '17 at 16:41

0

This is an alternative one

  cout.write((0==n)?("12"):((1==n)?("02"):("01")),2);

answered Nov 11 '17 at 16:41

iammosespaulr

9
1
4

3 implicit table/strings, 2 compares, less maintainable. I'm sorry, but putting everything on 1 line doesn't make it run faster or make it more maintainable. The reason @Geza's answer is so nice is that it has 0 compares and the lookups he includes are very plain to see. – Michael Dorgan Nov 13 '17 at 18:00

How do I optimize* this?

4 Answers4