LeetCode | Copy List with Random Pointer

package com.wzystal.day0710;

import java.util.HashMap;

/**
* Copy List with Random Pointer
* @author wzystal
*/
public class Solution {
class RandomListNode {
int label;
RandomListNode next, random;

public RandomListNode(int x) {
this.label = x;
}
}

// 时间复杂度O(n),空间复杂度O(n)
public RandomListNode copyRandomList1(RandomListNode head) {
if (head == null)
return head;
HashMap<RandomListNode, RandomListNode> map = new HashMap<>();
RandomListNode newHead = new RandomListNode(head.label);
map.put(head, newHead);
RandomListNode pre = newHead;
RandomListNode node = head.next;
while (node != null) {
RandomListNode newNode = new RandomListNode(node.label);
map.put(node, newNode);
pre.next = newNode;
pre = pre.next;
node = node.next;
}
node = head;
RandomListNode copyNode = newHead;
while (node != null) {
copyNode.random = map.get(node.random);
copyNode = copyNode.next;
node = node.next;
}
return newHead;
}

// 时间复杂度O(n),空间复杂度O(1)
public RandomListNode copyRandomList2(RandomListNode head) {
if (head == null)
return head;
RandomListNode node = head;
while (node != null) {
RandomListNode newNode = new RandomListNode(node.label);
newNode.next = node.next;
node.next = newNode;
node = newNode.next;
}
node = head;
while (node != null) {
if (node.random != null) {
node.next.random = node.random.next;
}
node = node.next.next;
}
RandomListNode newHead = head.next;
node = head;
while (node != null) {
RandomListNode newNode = node.next;
node.next = newNode.next;
if (newNode.next != null) {
newNode.next = newNode.next.next;
}
node = node.next;
}
return newHead;
}
}