本文首發於個人Githubnode
鏈表存儲有序的元素集合,但不一樣於數組,鏈表中的元素在內存中不是連續放置的。每一個元素由一個存儲元素自己的節點和指向下一個元素的 引用 組成。git
------------------------------------------------------------------------
| |
| node node null |
| --------------- --------------- -------- |
| head -> + item | next + -> + item | next + -> + null + |
| --------------- --------------- -------- |
| |
------------------------------------------------------------------------
複製代碼
class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}
class LinkList {
constructor() {
this.head = null;
this.length = 0;
}
/** * 添加節點 * @param {*} value */
append(value) {
return this.insert(value, this.length);
}
/** * 添加節點到指定位置 * @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; } /** * 移出指定位置的節點 * @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; } /** * 查找給定值所在索引 * @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; } } 複製代碼
題目:輸入一個單鏈表,輸出此鏈表中的倒數第 K 個節點。(去除頭結點,節點計數從 1 開始)。github
倒數第 k 個節點即爲整數第 n - k 個節點(n 爲鏈表長度)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; } 複製代碼
單鏈表中的環是指鏈表末尾的節點的 next 指針不爲 NULL ,而是指向了鏈表中的某個節點,致使鏈表中出現了環形結構。數組
0 -> 1 -> 2 -> 3 -> 4
| |
6 <- 5
複製代碼
鏈表中尾節點 6
指向了 節點 3
而非 null
,致使出現了環形結構。app
null
,但如果有環,2 指針一定在一個節點處相遇,該節點不爲 null
/** * 判斷鏈表是否存在環 * @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;
}
複製代碼
定位環的起點。oop
定義2個快慢指針,第一次先找到 2 個指針在環中的相遇點,而後令 p1 指向 相遇點,p2 指向頭節點,同時出發(每次走過的節點相同),當 2 指針指向的節點相同時,p1 即爲環的起點。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;
}
複製代碼