Question

Key | Data
----------
 1  |  A
 2  |  B
 3  |  C

Is there a data structure that allows me to lookup the data when given the key, or to lookup the key when given the data? I’m working in PHP, but I’m curious about answers for any language.

Answer 1

If you have it in an array..

$array = array('1'=>'A','2'=>'B','3'=>'C');

//Use the key to get the value
echo $array['1'] //Echos A
echo $array['2'] //Echos B
echo $array['3'] //Echos C

//Use the value to get the key
echo array_search('A',$array) //Echos 1
echo array_search('B',$array) //Echos 2
echo array_search('C',$array) //Echos 3