Merge branch 'master' of github.com:drbaggy/perlweeklychallenge-club

1 files changed, 50 insertions, 5 deletions

diff --git a/challenge-148/james-smith/README.md b/challenge-148/james-smith/README.md
index bd31e18284..785b3c233d 100644
--- a/challenge-148/james-smith/README.md
+++ b/challenge-148/james-smith/README.md
@@ -20,10 +20,48 @@ https://github.com/drbaggy/perlweeklychallenge-club/tree/master/challenge-148/ja
 
 ## The solution
 
+I will present two different solutions for the more general problem of large Eban numbers, but for numbers less than 1,000 we have:
+
+* The units must be 0, 2, 4, 6
+* The tens must be 0, 30, 40,50, 60, 
+
+So to compute the eban numbers less than 100 (and consequently all eban numbers less than one thousand) we can use:
+
+```perl
+say for map{my$a=$_;map{10*$a+2*$_||()}(0..3)}(0,3..6);
+```
+
+The `||()` removes the zero value which is not an eban number.
+
+This gives us the following numbers less than 1,000:
+
+`2 4 6 30 32 34 36 40 42 44 46 50 52 54 56 60 62 64 66`
+
+Now we can use this sequence to generate all eban numbers.
+
+For eban numbers of order *1000^n* we just need to multiply all the eban numbers of order "*1000^(n-1)*" these by 1000 and add each one add each of the eban numbers less than 100 (this time including 0). This assumes that for values of 1000, 1000000 etc we say *one thousand*, *one million*, ...
+
 ```perl
+say for my@e=grep{$_}my@n=map{my$a=$_;map{10*$a+2*$_}(0..3)}(0,3..6);
+for(2..$N){
+  say for@e=map{my$a=$_;map{$a*1e3+$_}@n}@e;
+}
 ```
 
-### Notes:
+The second removes the need to use `sprintf` everytime in the subsequent loops, by generating the list of numbers padded with 0s - we can see this with the performance gain in all but the first case (the first loop is made slightly more complex).
+
+### Notes: Timings
+
+| Max   | (in words)  | Rate            | Count      |
+| ----: | :---------: | --------------: | ---------: |
+|  10^3 | Thousand    |   200,481.00 /s |         19 |
+|  10^6 | Million     |    18,214.94 /s |        399 |
+|  10^9 | Billion     |       971.82 /s |      7,999 |
+| 10^12 | Trillion    |        49.41 /s |    159,999 |
+| 10^15 | Quadrillion |         2.27 /s |  3,199,999 |
+| 10^18 | Quintillion |         0.10 /s | 63,999,999 |
+
+Larger values of *n* would require too much memory to compute and alternative solution would be required {using seek etc to rewind the file}
 
 # Challenge 2 - Cardano Triplets
 ***Write a script to generate first 5 Cardano Triplets. A triplet of positive integers (a,b,c) is called a Cardano Triplet if it satisfies the below condition.***
@@ -42,7 +80,7 @@ Which can be further parametrized as:
 
 *b^2.c = k^2 . (8.k-3)*
 
-Where *a=3.k-1* *k* starts at 1.
+Where *a=3.k-1*. *k* starts at 1.
 
 So the first entry *k=1*, *b^2.c=5* - so is solved by *a=2*, *b=1*, *c=5*.
 
@@ -54,14 +92,21 @@ for my $k (1..3333) {
     say join "\t", 3*$k-1, $b, $n/$b/$b unless $n%($b*$b);
   }
 }
+```
 
 We loop through each value of `$k` up to 3,333, this gives the maximum value of `$a` 9,998. Largest less than or equal to 10,000.
 We then loop `$b` from 1 up to the value where `$c < 1`. Rather than computing `$c` at this stage (there could be rounding errors).
 We just compare the numerator (*k^2 . (8.k-3)*) with the denominator (*b^2*). We then check to see `$c` is an integer - we again
 do this without computing `$c` to avoid rounding errors - to compute the results and display them.
 
-Time taken to caluclate these **32,235** cardano triplets is **78.5sec**.
+Time taken to calculate these **32,235** cardano triplets is **78.5sec**.
 
-```
-### The result
+If we go back to the original problem and look at the first 5 cardano triplets we have either:
+
+The first 5 (if you sort by *a* and *b*) are:
+
+    (2,1,5), (5,1,52), (5,2,13), (8,1,189), (8,3,21).
+
+The first 5 (if you sort by total *a+b+c*) are:
 
+    (2,1,5), (5,2,13), (8,3,21), (17,18,5), (11,4,29).