PHP Array -- PHP 实现堆栈 PHP Stack

"堆栈" 遵循后入现出的原则（LIFO）

PHP提供 array_push() 和 array_pop()函数，可以利用数组实现基本堆栈操作。

下面是一个提供全部堆栈常用操作的函数库。

 

// 来自 PHP5 in Practice  (U.S.)Elliott III & Jonathan D.Eisenhamer

 <?php // A library to implement stacks in PHP via arrays // The Initialize function creates a new stack: function &stack_initialize() { // In this case, just return a new array $new = array(); return $new; } // The destory function will get rid of a stack function stack_destroy(&$stack) { // Since PHP is nice to us, we can just use unset unset($stack); } // The push operation on a stack adds a new value unto the top of the stack function stack_push(&$stack, $value) { // We are just adding a value to the end of the array, so can use the // [] PHP Shortcut for this. It's faster than usin array_push $stack[] = $value; } // Pop removes the top value from the stack and returns it to you function stack_pop(&$stack) { // Just use array pop: return array_pop($stack); } // Peek returns a copy of the top value from the stack, leaving it in place function stack_peek(&$stack) { // Return a copy of the value on top of the stack (the end of the array) return $stack[count($stack)-1]; } // Size returns the number of elements in the stack function stack_size(&$stack) { // Just using count will give the proper number: return count($stack); } // Swap takes the top two values of the stack and switches them function stack_swap(&$stack) { // Calculate the count: $n = count($stack); // Only do anything if count is greater than 1 if ($n > 1) { // Now save a copy of the second to last value $second = $stack[$n-2]; // Place the last value in second to last place: $stack[$n-2] = $stack[$n-1]; // And put the second to last, now in the last place: $stack[$n-1] = $second; } } // Dup takes the top value from the stack, duplicates it, // and adds it back onto the stack function stack_dup(&$stack) { // Actually rather simple, just reinsert the last value: $stack[] = $stack[count($stack)-1]; } // Let's use these to create a small stack of data and manipulate it. // Start by adding a few numbers onto it, making it: 73 74 5 $mystack =& stack_initialize(); stack_push($mystack, 73); stack_push($mystack, 74); stack_push($mystack, 5); // Now duplicate the top, giving us: 73 74 5 5 stack_dup($mystack); // Check the size now, it should be 4 echo '<p>Stack size is: ', stack_size($mystack), '</p>'; // Now pop the top, giving us: 5 echo '<p>Popped off the value: ', stack_pop($mystack), '</p>'; // Next swap the top two values, leaving us with: 73 5 74 stack_swap($mystack); // Peek at the top element to ensure it is 74 echo '<p>Current top element is: ', stack_peek($mystack), '</p>'; // Now destroy it, we are done. stack_destroy($mystack); ?>