PHP stack data structure and parentheses matching algorithm example explained

This paper mainly introduces the PHP implementation of the stack data structure and the matching algorithm, combined with examples of PHP array operation to implement the stack data structure, stack, and stack-based brace matching application skills, the need for friends can refer to, hope to help everyone.

Stack, the embodiment is LIFO, that is, LIFO. Queue, which embodies FIFO.

Stack operation:

Array_pop ()//Tail out Array_push ()//Lujin

Or

Array_shift ()//head into Array_unshift ()//head out

Use case: Verify that a mathematical formula is correct, such as {2*3[x*y+5+m* (i-j)/3]+k* (4+ (t+9))}.

Analysis: For a calculation of the correct or not, is the body now, the matching of the various parentheses, the parentheses exactly match, the calculation is no problem, how to test a formula in the matching of parentheses, met a lot of people think of using the regular. I can't figure out how this is going to be written, how to implement nested relationships. This time the stack will come in handy. Look at the code below.

function Checkmatch ($STR) {if (! $str) return false;  $arr = Str_split ($STR);  $left = Array (' {', ' [', ' (');  $right = Array ('} ', '] ', ') ');  $stack = Array ();  Reset ($arr); Using the while traversal array requires reset () to prevent traversal of incomplete while (list ($key, $val) = each ($arr)) {if (In_array ($val, $left, True)) {//into the Stack AR Ray_push ($stack, $val); Put all the left brackets that appear in the stack}else if (In_array ($val, $right, True)) {$topStack = end ($stack);//If a closing parenthesis appears, the element at the top of the stack must be the opening parenthesis that matches it (because the parentheses are the corresponding      ), first remove the top element of the stack. if (Isset ($topStack) &&!empty ($topStack)) {if (Array_search ($val, $right, true) = = = Array_search ($topStack, $le Ft,true) {//To determine if the current closing parenthesis matches the left parenthesis//out of the stack Array_pop ($stack);//Match the pop out of the stack}else{//RE Turn false; Left/Right mismatch}}else{//return FALSE;//closing parenthesis Many, because the corresponding opening parenthesis}}} return empty ($stack)?  True:false; After the completion of the cycle to determine whether there is a value in $stack, there are words to prove that the left parenthesis more} $test = ' {2*3[x*y+5+m* (i-j)/3]+k* (4+ (t+9))} '; Var_dump (Checkmatch ($test)); 

The stacks in the above code are implemented by Array_pop and Array_push, as well as by Array_shift and Array_unshift.

Attached: Queue operations

Array_shift ()//head out Array_push ()//Lujin

Or

Array_unshift//Head in Array_pop//tail out

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