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Stack.js
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67 lines (59 loc) 路 1.57 KB
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import LinkedList from '../linked-list/LinkedList';
export default class Stack {
constructor() {
// We're going to implement Stack based on LinkedList since these
// structures are quite similar. Compare push/pop operations of the Stack
// with prepend/deleteHead operations of LinkedList.
this.linkedList = new LinkedList();
}
/**
* @return {boolean}
*/
isEmpty() {
// The stack is empty if its linked list doesn't have a head.
return !this.linkedList.head;
}
/**
* @return {*}
*/
peek() {
if (this.isEmpty()) {
// If the linked list is empty then there is nothing to peek from.
return null;
}
// Just read the value from the start of linked list without deleting it.
return this.linkedList.head.value;
}
/**
* @param {*} value
*/
push(value) {
// Pushing means to lay the value on top of the stack. Therefore let's just add
// the new value at the start of the linked list.
this.linkedList.prepend(value);
}
/**
* @return {*}
*/
pop() {
// Let's try to delete the first node (the head) from the linked list.
// If there is no head (the linked list is empty) just return null.
const removedHead = this.linkedList.deleteHead();
return removedHead ? removedHead.value : null;
}
/**
* @return {*[]}
*/
toArray() {
return this.linkedList
.toArray()
.map(linkedListNode => linkedListNode.value);
}
/**
* @param {function} [callback]
* @return {string}
*/
toString(callback) {
return this.linkedList.toString(callback);
}
}