Re: Challenge 1 - Triangle Font - KX Learning Hub

SJT

Member
February 2, 2023 at 12:00 am
BaiChens solution uses the Scan form of the Do iterator rather than the Each iterator ' I used.

Terse q helps us focus on the core of the algorithm. Lets use BaiChens solution as a practice example.

We can rewrite to eliminate the local variable. And, all other things being equal, good q style prefers infix syntax to bracket notation.
```
q)8{first[x+1]#x+1}1 
1 
2 2 
3 3 3 
4 4 4 4 
5 5 5 5 5 
6 6 6 6 6 6 
7 7 7 7 7 7 7 
8 8 8 8 8 8 8 8 
9 9 9 9 9 9 9 9 9
```
The addition surely only needs doing once?
```
q)4{first[b]#b:x+1}1 
1 
2 2 
3 3 3 
4 4 4 4 
5 5 5 5 5
```
On each iteration the vector argument lengthens. But we need increment only its first item.
```
q)4{b#b:1+first x}1 
1 
2 2 
3 3 3 
4 4 4 4 
5 5 5 5 5
```
The pattern N f1 is easily recognisable as: Do f N times, starting with 1.

Tightening up the algorithm saves CPU, but the Each is faster still.
```
q)ts:10000 {b:first x+1;b#x+1}[100;1] 
438 64560 
q)ts:10000 100{b#b:1+first x}1 
301 63536 
q)ts:10000 {x#'x} 1+til 100 
174 63616
```
On the next episode of the Array Cast (just recorded on Tuesday), Michael Higginson talks about how the terse and interactive APL and q REPLs encourage him to compare multiple solutions in a way he would rarely have time to do when writing Java.