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链表存储有序的元素集合,但不一样于数组,链表中的元素在内存中不是连续放置的。每一个元素由一个存储元素自己的节点和指向下一个元素的 引用 组成。git
------------------------------------------------------------------------
| |
| node node null |
| --------------- --------------- -------- |
| head -> + item | next + -> + item | next + -> + null + |
| --------------- --------------- -------- |
| |
------------------------------------------------------------------------
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class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}
class LinkList {
constructor() {
this.head = null;
this.length = 0;
}
/** * 添加节点 * @param {*} value */
append(value) {
return this.insert(value, this.length);
}
/** * 添加节点到指定位置 * @param {*} value * @param {*} position */
insert(value, position) {
if (position < 0 || position > this.length) {
return false;
}
let node = new Node(value);
if (position === 0) {
node.next = this.head;
this.head = node;
} else {
let prev = null;
let current = this.head;
let i = 0;
while (i++ < position) { prev = current; current = current.next; } prev.next = node; node.next = current; } this.length++; return true; } /** * 移出指定位置的节点 * @param {*} position */ removeAt(position) { if (position < 0 || position > this.length) { return false; } if (position === 0) { this.head = this.head.next; } else { let prev = null; let current = this.head; let i = 0; while (i++ < position) { prev = current; current = current.next; } prev.next = current.next; } this.length--; return true; } /** * 查找给定值所在索引 * @param {*} value */ indexOf(value) { let current = this.head; let index = -1; while (current) { indeex++; if (current.value === value) { return index; } else { current = current.next; } } return -1; } reverse() { let prev = null; let current = this.head; let next = null; while (current) { next = current.next; current.next = prev; prev = current; current = next; } this.head = prev; } traverseFromTailToHead() { let stack = []; let current = this.head; while (current) { stack.push(current); current = current.next; } while (stack.length) { stack.pop(); } } getKthNodeFromTailToHead(k) { let p1 = this.head; let p2 = this.head; let i = 0; while (i++ < k) { p1 = p1.next; } while (p1) { p1 = p1.next; p2 = p2.next; } return p2; } } 复制代码
题目:输入一个单链表,输出此链表中的倒数第 K 个节点。(去除头结点,节点计数从 1 开始)。github
倒数第 k 个节点即为整数第 n - k 个节点(n 为链表长度)shell
function findKthTail(linkList, k) {
let p1 = linkList.head;
let p2 = linkList.head;
let i = 0;
while (i++ < k) { p1 = p1.next; } while (p1) { p1 = p1.next; p2 = p2.next; } return p2; } 复制代码
单链表中的环是指链表末尾的节点的 next 指针不为 NULL ,而是指向了链表中的某个节点,致使链表中出现了环形结构。数组
0 -> 1 -> 2 -> 3 -> 4
| |
6 <- 5
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链表中尾节点 6
指向了 节点 3
而非 null
,致使出现了环形结构。app
null
,但如果有环,2 指针一定在一个节点处相遇,该节点不为 null
/** * 判断链表是否存在环 * @param {*} linkList */
function isExistLoop(linkList) {
let p1 = linkList.head;
let p2 = linkList.head;
while (p1 && p2.next) {
p1 = p1.next;
p2 = p2.next.next;
if (p1 === p2) {
return true;
}
}
return false;
}
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定位环的起点。oop
定义2个快慢指针,第一次先找到 2 个指针在环中的相遇点,而后令 p1 指向 相遇点,p2 指向头节点,同时出发(每次走过的节点相同),当 2 指针指向的节点相同时,p1 即为环的起点。this
function getMeetingNode(linkList) {
let p1 = linkList.head;
let p2 = linkList.head;
while (p1 && p2.next) {
p1 = p1.next;
p2 = p2.next.next;
if (p1 == p2) {
return p1;
}
}
return null;
}
function getEntryOfLoop(linkList) {
let meetingNode = linkList.getMeetingNode();
if (!meetingNode) {
return null;
}
let p1 = meetingNode;
let p2 = linkList.head;
while (p1 != p2) {
p1 = p1.next;
p2 = p2.next;
}
return p1;
}
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