Google's interview topic everyone to try the solution

Google's interview topic everyone to try
An algorithm problem, and search suggestions related, I have been engaged for a long time did not get out, have the ability to try, I basically say the topic
Array A={a,b,c,d,e,f}
Array B={u,y,w,x,y,z}
The output string rules are as follows:
A
U
Ab
Uy
Ay
Ub
Abc
Uyw
Abw
ByT
Ubc
Uyc
ByT
Ubw
.
.
.
Find the law first, then the algorithm, the algorithm language is not limited





------Solution--------------------

PHP Code

$a = Array (' A ', ' B ', ' C ', ' d ', ' e ', ' f '); $b = Array (' u ', ' Y ', ' w ', ' x ', ' y ', ' z '); $r = Array (); for ($i =0; $i
  
  

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