Copy List with Random Pointer

Copy List with Random Pointer

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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.

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这个题目，其实挺简单的，要把原链表的每一个元素都拷贝一遍，不能拷贝多，也不能少拷贝。使用set和map可以，知道原来链表当中的节点是否访问过，没有就new一个节点，并以原链表节点为key，新链表节点为值存储起来，以后可能会用到。所以就以第一个节点为起始点，每次查询这个节点的random和next如果，这两个节点在拷贝链表当中没有对应的，那就new新的。有就直接取出来，然后对random和next建立相关连接信息。

/** * 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) {        Map<RandomListNode,RandomListNode> set1 = new HashMap<RandomListNode,RandomListNode> ();        Map<RandomListNode,RandomListNode> set2 = new HashMap<RandomListNode,RandomListNode> ();        RandomListNode r1,r2,r3,r4,r5,r6;        if(head==null)        return null;        RandomListNode newHead = new RandomListNode(head.label);        r1 = newHead;        set1.put(head, head);        set2.put(head, newHead);        while(head!=null)        {        //make r1 to equals to head                if(!set1.containsKey(head))        {        set1.put(head, head);        r1 = new RandomListNode(head.label);        set2.put(head, r1);        }else        {        r1 = set2.get(head);        }        // make r3 equals to head next;        r2 = head.next;        if(r2!=null)        {        if(!set1.containsKey(r2))        {        set1.put(r2, r2);        r3 = new RandomListNode(r2.label);        set2.put(r2,r3);        }else{            // this place is set2        r3 = set2.get(r2);        }        }else        {        r3 = null;        }        // set t.next as r3        r1.next = r3;        //make r5 equals to head.random        r4 = head.random;        if(r4!=null)        {        if(!set1.containsKey(r4))        {        set1.put(r4, r4);        r5 = new RandomListNode(r4.label);        set2.put(r4, r5);        }else {r5 = set2.get(r4);}        }else        {        r5 = null;        }        r1.random = r5;        head = head.next;        }        return newHead;    }}