Strings Are Arrays
I’ve seen a lot of people asking questions about how to find a certain character or sequence inside a string. It is common for people to turn to the library in order to find a function that does this for them, but it is likely the case that the answer is right in front of you. If you need to search thorough a string for whatever reason you can index it as an array. This is the case in a lot of language (PHP, C++, Java).
In a non-type-safe language like PHP people often forget the distinction between primitive types and other constructs. Primitives are often things like int, float, double, long, and char. Strings are generally not a primitive type but an array of chars. Most languages tend to hide this fact from you, because strings are so common it is often more convenient for the programmer to deal with them as if they were not an array of characters. For example, Java does not support operator overloading; you can only use arithmetic operators (+, -, *) on primitive types, with the exception of strings, which can be appended using the + operator.
So how can you use this fact to your advantage? There are many cases where indexing strings rather than passing them to some function can serve your purpose more efficiently. Here are some examples in PHP:
Ex.
You have several lines of text and you want to count the instances of a particular word. One way to do this would be to use explode to turn the text into an array of words and then count the instances of that word:
$text = 'cat dog chicken cat bird mouse cat lizard';
$words = explode(' ' , $text);
$count = 0;
foreach($words as $word)
{
if($word == 'cat')
$count++;
}
echo $count; //should output 3
One function call and one loop, pretty simple right? Maybe not. It is important to remember that function calls may a lot more than they appear. In order to split the string into an array of words, explode must search through the string for a space. If all you need to do is count the number of instances of a word, there is no need to waste time constructing an array of words and then looping through that array. Here is a more efficient way:
$curr = '';
$count = 0;
$searchStr = 'cat';
$text = 'cat dog chicken cat bird mouse cat lizard';
$len = strlen($text);
for($i = 0; $i < $len; $i++)
{
if($text[$i] == ' ')
{
if($curr == $searchStr)
$count++;
$curr = '';
}
else
$curr .= $text[$i];
}
The above example contains several more lines of code, but it is important to remember that the number of lines in a program should not be used to measure the performance of a program.