算法步骤:
- 第 1 步:先将待反转的区域反转;
- 第 2 步:把 pre 的 next 指针指向反转以后的链表头节点,把反转以后的链表的尾节点的 next 指针指向 succ。
一些技巧:
- 因为头节点有可能发生变化,使用虚拟头节点可以避免复杂的分类讨论
const dummyNode = new ListNode(-1);dummyNode.next = head;
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} head
* @param {number} left
* @param {number} right
* @return {ListNode}
*/
var reverseBetween = function(head, left, right) {
const dummyNode = new ListNode(-1);
dummyNode.next = head;
let pre = dummyNode;
// step1:从虚拟头节点走left-1步,找到pre 和left
for(let i=0;i<left-1;i++){
pre = pre.next;
}
let leftNode = pre.next;
// step2:从pre再走right-left+1步,找到right和succ
let rightNode = pre;
for(let i=0;i<right-left+1;i++){
rightNode = rightNode.next;
}
let succ = rightNode.next;
// step3:切断子链表的连接
pre.next = null;
rightNode.next = null;
// step4: 反转链表子区间
reverseLinkedList(leftNode);
// step5:接回原来的链表中
pre.next = rightNode;
leftNode.next = succ;
return dummyNode.next;
};
const reverseLinkedList = function(head){
let pre = null;
let cur = head;
while(cur){
const tmp = cur.next;
cur.next = pre;
pre = cur;
cur = tmp;
}
};
编写链表测试程序
包括构建链表与打印链表
// 定义单链表
function ListNode(val){
this.val = val;
this.next = null;
}
// 通过一个长度为n的数组创建链表
var createLinkedList = function(arr,n){
if(n===0){
return null;
}
let head = new ListNode(arr[0]);
let curNode = head;
for(let i=1;i<n;i++){
curNode.next = new ListNode(arr[i]);
curNode = curNode.next;
}
return head;
}
// 打印链表
var printLinkedList = function(head){
let curNode = head;
let printList = '';
while(curNode !== null){
printList += `${curNode.val}->`;
curNode = curNode.next;
}
printList += `NULL`;
console.log(printList);
return;
}
// test
let arr = [5,2,9,0,3];
let n = arr.length;
let head = createLinkedList(arr,n);
printLinkedList(head);