[数据结构学习笔记5] 堆栈（Stack）

堆栈，我们总是把新的数据加在堆栈的最顶端，移除的时候也是从最顶端开始移除。也叫LIFO（last in first out）。

Push: 1

Stack: 1

Push: 2

Stack: 2, 1

Push: 3

Stack: 3, 2, 1

Pop()

Stack: 2, 1

Pop()

Stack: 1

 

代码实现（javascript）

class Stack {
  constructor(... items) {
       this.items = items;      
    }  

   clear() {
        this.items.length = 0;
    }

   clone() {
        return new Stack(...this.items);  
    }  

  contains(item) {
        return this.items.includes(item);
    }  

  peek() {
        let itemsLength = this.items.length;
        let item = this.items[itemsLength - 1];

        return item;        
    }  

  pop() {
        let removedItem = this.items.pop();
        return removedItem;    
    }  

  push(item) {
         this.items.push(item);
         return item; 
      }  
}

使用Stack()

let myStack = new Stack();

// Add items
myStack.push("One");
myStack.push("Two");
myStack.push("Three");

// Preview the last item
myStack.peek(); // Three

// Remove item
let lastItem = myStack.pop();
console.log(lastItem); // Three

myStack.peek(); // Two

// Create a copy of the stack
let newStack = myStack.clone();

// Check if item is in Stack
newStack.contains("Three"); // false

时间复杂度

动作	最佳	平均	最差
Push	O(1)	O(1)	O(1)
Pop	O(1)	O(1)	O(1)
Peek	O(1)	O(1)	O(1)
Search/Contains	O(1)	O(n)	O(n)
Memory	O(n)	O(n)	O(n)