/**
143. Reorder List
https://leetcode.com/problems/reorder-list/description/
* @param {ListNode} head
* @return {void} Do not return anything, modify head in-place instead.
*/
var reorderList = function (head) {
if (head==null || head.next==null)
return;
//1.find the middle of list
let middle = findMiddle(head);
let secondHead = middle.next;
middle.next = null;//断开中点和后一段
//2.reserve it
let reverseSecondHead = reverseLinkedList(secondHead);
//3.merge two list by items one by one
return mergeLinkedList(head,reverseSecondHead);
};
var findMiddle = function (head) {
let slow = head, fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
}
return slow;
};
var reverseLinkedList = function (head) {
let prev = null;
let next = null;
let current = head;
while (current != null) {
next = current.next;
current.next = prev;//point to prve
prev = current;
current = next;
}
return prev;
};
var mergeLinkedList = function (node1,node2) {
//将第二个链表的元素间隔地插入第一个链表中
let cur = node1;
while (node2!=null){
let temp = node2.next;
node2.next = cur.next;
cur.next = node2;
cur = cur.next.next;
node2 = temp;
}
};