1 <?php 2 #设计一个栈的数据结构，要求增加一个min函数，可以取出栈的最小元素 3 #要求push,pop,min的时间复杂度都是O(1) 4 #解题思路：在每个栈元素增加一个min变量，这个变量存储次元素及其之前所有元素的最小值 5 6 #栈节点 7 class Node { 8 public $data = null; 9 public $min = null; 10 } 11 12 class Min_Stack { 13 private $data = array(); 14 private $top; 15 16 public function __construct(Array $a) { 17 $this->top = 0; 18 foreach($a as $val) { 19 $this->push($val); 20 } 21 } 22 23 public function push($i) { 24 $node = new Node(); 25 $node->data = $i; 26 27 #此处设置每个节点的min值，设置方法为若栈为空，当前元素data则为当前节点的min 28 #若栈非空，则当前元素data与前一个节点的min值比较，取其小者作为当前节点的min 29 if ($this->top == 0) { 30 $min = $node->data; 31 } else { 32 $min = $this->data[$this->top - 1]->min < $node->data ? $this->data[$this->top - 1]->min : $node->data; 33 } 34 35 $node->min = $min; 36 $this->data[] = $node; 37 $this->top++; 38 return $node; 39 } 40 41 public function pop() { 42 $r = $this->data[--$this->top]; 43 unset($this->data[$this->top]); 44 return $r; 45 } 46 47 public function get_min() { 48 return $this->data[$this->top - 1]->min; 49 } 50 } 51 52 $a = array(5, 7, 3, 8, 9, 1, 2); 53 $min_stack = new Min_Stack($a); 54 echo "Min : {$min_stack->get_min()} <br>"; 55 print_r($min_stack); 56 echo "<br> Pop : {$min_stack->pop()->data}<br>"; 57 print_r($min_stack); 58 ?>
Min : 1
Min_Stack Object ( [data:Min_Stack:private] => Array ( [0] => Node Object ( [data] => 5 [min] => 5 ) [1] => Node Object ( [data] => 7 [min] => 5 ) [2] => Node Object ( [data] => 3 [min] => 3 ) [3] => Node Object ( [data] => 8 [min] => 3 ) [4] => Node Object ( [data] => 9 [min] => 3 ) [5] => Node Object ( [data] => 1 [min] => 1 ) [6] => Node Object ( [data] => 2 [min] => 1 ) ) [top:Min_Stack:private] => 7 )
Pop : 2
Pop : 1
Min : 3
Min_Stack Object ( [data:Min_Stack:private] => Array ( [0] => Node Object ( [data] => 5 [min] => 5 ) [1] => Node Object ( [data] => 7 [min] => 5 ) [2] => Node Object ( [data] => 3 [min] => 3 ) [3] => Node Object ( [data] => 8 [min] => 3 ) [4] => Node Object ( [data] => 9 [min] => 3 ) ) [top:Min_Stack:private] => 5 )
