CopyListwithRandomPointer

Change-Id: I9bbb3d92586800a06fa3890b32643be564def72f

CopyListwithRandomPointer.java

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+/*
+ Author:     Andy, [email protected]
+ Date:       Jan 13, 2015
+ Problem:    Copy List with Random Pointer
+ Difficulty: Easy
+ Source:     http://oj.leetcode.com/problems/copy-list-with-random-pointer/
+ Notes:
+ 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.
+
+ Solution:  1. HashMap
+            2. uses constant extra space.
+            3. Recursive. (Stack)-->StackOverflow in Java.
+            4. Iterative. (Queue)
+*/
+/**
+ * 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_1(RandomListNode head) {
+        if (head == null) return null;
+        HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
+        RandomListNode dummy = new RandomListNode(-1);
+        RandomListNode curNew = dummy, cur = head;
+        while (cur != null) {
+            if (map.containsKey(cur) == false) {
+                map.put(cur, new RandomListNode(cur.label));
+            }
+            if (cur.random != null && map.containsKey(cur.random) == false) {
+                map.put(cur.random, new RandomListNode(cur.random.label));
+            }
+            curNew.next = map.get(cur);
+            curNew.next.random = map.get(cur.random);
+            curNew = curNew.next;
+            cur = cur.next;
+        }
+        return dummy.next;
+    }
+    public RandomListNode copyRandomList_2(RandomListNode head) {
+        if (head == null) return null;
+        RandomListNode cur = head;
+        while (cur != null) {
+            RandomListNode newnode = new RandomListNode(cur.label);
+            newnode.next = cur.next;
+            cur.next = newnode;
+            cur = cur.next.next;
+        }
+        cur = head;
+        while (cur != null) {
+            if (cur.random != null) {
+                cur.next.random = cur.random.next;
+            }
+            cur = cur.next.next;
+        }
+        RandomListNode dummy = new RandomListNode(-1);
+        RandomListNode curNew = dummy;
+        cur = head;
+        while (cur != null) {
+            curNew.next = cur.next;
+            curNew = curNew.next;
+            cur.next = cur.next.next;
+            cur = cur.next;
+        }
+        return dummy.next;
+    }
+    public RandomListNode copyRandomList_3(RandomListNode head) {/*StackOverflowError*/
+        if (head == null) return null;
+        HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
+        return copy(head, map);
+    }
+    public RandomListNode copy(RandomListNode root, HashMap<RandomListNode, RandomListNode> map) {
+        if (root == null) return null;
+        if (map.containsKey(root) == true) {
+            return map.get(root);
+        }
+        RandomListNode newnode = new RandomListNode(root.label);
+        map.put(root, newnode);
+        newnode.next = copy(root.next, map);
+        newnode.random = copy(root.random, map);
+        return newnode;
+    }
+    public RandomListNode copyRandomList_4(RandomListNode head) {
+        if (head == null) return null;
+        HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
+        Queue<RandomListNode> queue = new LinkedList<RandomListNode>();
+        queue.offer(head);
+        map.put(head, new RandomListNode(head.label));
+        while (queue.isEmpty() == false) {
+            RandomListNode cur = queue.poll();
+            if (cur.next != null && map.containsKey(cur.next) == false) {
+                RandomListNode newnode = new RandomListNode(cur.next.label);
+                map.put(cur.next, newnode);
+                queue.offer(cur.next);
+            }
+            map.get(cur).next = map.get(cur.next);
+            if (cur.random != null && map.containsKey(cur.random) == false) {
+                RandomListNode newnode = new RandomListNode(cur.random.label);
+                map.put(cur.random, newnode);
+                queue.offer(cur.random);
+            }
+            map.get(cur).random = map.get(cur.random);
+        }
+        return map.get(head);
+    }
+}