代码随想录算法训练营第三天 | 203、707、206

算法
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203. 移除链表元素

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package main

// Definition for singly-linked list.
type ListNode struct {
    Val  int
    Next *ListNode
}

func removeElements(head *ListNode, val int) *ListNode {
    dummy := &ListNode{Next: head}
    cur := dummy

    for cur.Next != nil {
        if cur.Next.Val == val {
            cur.Next = cur.Next.Next
        } else {
            cur = cur.Next
        }
    }

    return dummy.Next
}

707. 设计链表

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package main

type Node struct {
    Val  int
    Next *Node
}

type MyLinkedList struct {
    dummyHead *Node
    size      int
}

func Constructor() MyLinkedList {
    return MyLinkedList{
        dummyHead: &Node{}, // 虚拟头节点
        size:      0,
    }
}

func (this *MyLinkedList) Get(index int) int {
    if index < 0 || index >= this.size {
        return -1
    }
    current := this.dummyHead.Next
    for i := 0; i < index; i++ {
        current = current.Next
    }
    return current.Val
}

func (this *MyLinkedList) AddAtHead(val int) {
    newNode := &Node{Val: val}
    newNode.Next = this.dummyHead.Next
    this.dummyHead.Next = newNode
    this.size++
}

func (this *MyLinkedList) AddAtTail(val int) {
    newNode := &Node{Val: val}
    current := this.dummyHead
    for current.Next != nil {
        current = current.Next
    }
    current.Next = newNode
    this.size++
}

func (this *MyLinkedList) AddAtIndex(index int, val int) {
    if index > this.size {
        return
    }
    if index < 0 {
        index = 0
    }
    prev := this.dummyHead
    for i := 0; i < index; i++ {
        prev = prev.Next
    }
    newNode := &Node{Val: val}
    newNode.Next = prev.Next
    prev.Next = newNode
    this.size++
}

func (this *MyLinkedList) DeleteAtIndex(index int) {
    if index < 0 || index >= this.size {
        return
    }
    prev := this.dummyHead
    for i := 0; i < index; i++ {
        prev = prev.Next
    }
    prev.Next = prev.Next.Next
    this.size--
}

206. 反转链表

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/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */

package main

func reverseList(head *ListNode) *ListNode {
    var prev *ListNode
    current := head
    for current != nil {
        next := current.Next // 保存下一个节点
        current.Next = prev  // 当前节点指向前驱
        prev = current       // 前驱节点后移
        current = next       // 当前节点后移
    }
    return prev
}