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day4-linked-list2.js
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day4-linked-list2.js
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class ListNode {
constructor(data, next = null) {
this.data = data
this.next = next
}
}
class LinkedList {
constructor() {
this.root = null
}
// 用以呈現linked list字串模樣
toString() {
let result = "root -> "
let current = this.root
while (current !== null) {
result += current.data + " -> "
current = current.next
}
return result + "null"
}
// 回傳linked list長度
length() {
// 從第一個節點開始
let current = this.root
let count = 0
while (current !== null) {
count++
// current移到下個節點
current = current.next
}
return count
}
// 判斷linked list是否有節點
isEmpty() {
return this.root === null
}
// 取得指定節點
get(index) {
let current = this.root
let count = 0
while (current !== null) {
if (count === index) {
return current.data
}
count++
current = current.next
}
return null
}
// 在linked list移除節點
removeAtIndex(index) {
// 避免不存在的索引值
if (index < 0 || index >= this.size) {
return;
}
if (index === 0) {
if (this.root !== null) {
this.root = this.root.next
}
} else {
let current = this.root
let i = 0
// 不斷從第一個節點往下找,直到current是目標刪除節點的前前個節點
while (current !== null && i < index - 1) {
i++
current = current.next
}
// 經過最後一次while迴圈,current是被刪除節點的前一個節點,直接指定current的下一個節點是後後個節點,跳過被刪除節點
current.next = current.next.next
}
}
// 在linked list增加節點
addAtIndex(index, data) {
// 在linked list最前面增加節點
if (index === 0) {
let node = new ListNode(data) // 產生新節點
node.next = this.root // 將新節點的指標指向原本第一個節點
this.root = node // 現在,換新節點是第一個節點了
this.size++
} else {
let current = this.root
let i = 0
while (current !== null && i < index - 1) {
i++
current = current.next
}
let node = new ListNode(data)
node.next = current.next
current.next = node
}
}
}
let list = new LinkedList()
list.addAtIndex(0, 1)
list.addAtIndex(0, 2)
list.addAtIndex(0, 3)
console.log(list.toString())
list.removeAtIndex(0)
console.log(list.toString())
list.addAtIndex(2, 4)
console.log(list.toString())