leetcode 138. Copy List with Random Pointer ----- java

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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.

 

和第133題差不多，都是圖的複製，區別在於這道題的label有可能是相同的，所以導致了map的key有可能相同，所以需要處理。

兩種方法差不多。第二種更簡潔。

 

1、在複製next之後修改原結構的label為順序增長，方便建立map，之後再修改回來。

/** * 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 null;        Map map2 = new HashMap<Integer,RandomListNode>();        int num = 1;        RandomListNode node = head;        RandomListNode newNode = new RandomListNode(head.label);        RandomListNode node2 = newNode;        map2.put(0,node2);        node.label = 0;        node = node.next;        while( node != null ){            RandomListNode nextNode = new RandomListNode(node.label);            node2.next = nextNode;            node2 = node2.next;            node.label = num;            map2.put(num,node2);            num++;            node = node.next;        }        node = head;        node2 = newNode;        while( node != null ){            if( node.random == null){                node = node.next;                node2 = node2.next;                continue;            }            node2.random = (RandomListNode) map2.get( node.random.label );            node = node.next;            node2 = node2.next;        }        node2 = newNode;        node = head;        while( node != null ){            node.label = node2.label;            node = node.next;            node2 = node2.next;        }        return newNode;            }}

2、建立map的時候使用

 Map<RandomListNode,RandomListNode>

 

/** * 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 null;        Map<RandomListNode,RandomListNode> map = new HashMap<RandomListNode,RandomListNode>();        RandomListNode node = head;        while( node != null ){            map.put(node,new RandomListNode(node.label));            node = node.next;        }        node = head;        while( node != null ){                        map.get(node).next = map.get(node.next);            map.get(node).random = map.get(node.random);            node = node.next;        }        return map.get(head);            }}

 

leetcode 138. Copy List with Random Pointer ----- java