【LeetCode】Copy List with Random Pointer

標籤：map   list   leetcode   

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

思路：第一遍正常複製鏈表，同時用雜湊表儲存鏈表中原始節點和新節點的對應關係，第二遍遍曆鏈表的時候，再複製隨機域。

這是一種典型的空間換時間的做法，n個節點，需要大小為O(n)的雜湊表，同時時間複雜度可以降低到O(n)。

/** * Definition for singly-linked list with a random pointer. * class RandomListNode { *     int label; *     RandomListNode next, random; *     RandomListNode(int x) { this.label = x; } * }; */public class Solution {    public RandomListNode copyRandomList(RandomListNode head) {        if (head == null) {return head;}HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();RandomListNode res = null;RandomListNode taiListNode = null;RandomListNode cur = head;while (cur != null) {if (res == null) {res = new RandomListNode(cur.label);res.next = res.random = null;taiListNode = res;map.put(head, res);}else{taiListNode.next = new RandomListNode(cur.label);taiListNode = taiListNode.next;map.put(cur, taiListNode);}cur = cur.next;}taiListNode.next = null;cur = head;taiListNode = res;while (cur != null) {taiListNode.random = (RandomListNode)map.get((RandomListNode)cur.random);cur = cur.next;taiListNode = taiListNode.next;}return res;    }}