哪个更快/更好地存储PHP中的字符串集合

Question

I am trying to create an array to store which nodes I have visited before. The nodes will be uniquely represented by a string, and the string can be very long. Hence, I am wondering which of the two implementations will be faster or more scalable.

$stateString = "..... ....";
$states = array();

1) Storing the stateString as a key

$states[$stateString] = true; // I just want to set the key in the array
$visited = isset($states[$stateString]);

2) Storing the stateString as a value

$states[] = $stateString;
$visited = in_array($stateString, $states);

Answer 1

Storing as a key is much faster (for the random look-ups you are talking about).