add code of 138

Author: Li Li

top-interview-questions/138. Copy List with Random Pointer.cs

@@ -0,0 +1,41 @@
+/*
+1. generate new nodes and make the maping old -> new
+2. loop the old, use map to get all random and next.
+ */
+public class Solution {
+    public RandomListNode CopyRandomList(RandomListNode head) {
+        if (head == null) return null;
+        Dictionary<RandomListNode, RandomListNode> dict = new Dictionary<RandomListNode,RandomListNode>();
+        GenerateAllNodesAndMapping(head, dict);
+        CopyList(head, dict);
+        return dict[head];
+    }
+    private void GenerateAllNodesAndMapping(RandomListNode head, Dictionary<RandomListNode, RandomListNode> dict) {
+        while (head != null) {
+            RandomListNode node = new RandomListNode(head.label);
+            dict.Add(head, node);
+            head = head.next;
+        }
+    }
+    private void CopyList(RandomListNode head, Dictionary<RandomListNode, RandomListNode> dict) {
+        while (head != null) {
+            RandomListNode temp = dict[head];
+            if (head.next != null) {
+                temp.next = dict[head.next];
+            } 
+            if (head.random != null) {
+                temp.random = dict[head.random];
+            }
+            head = head.next;
+        }
+    }
+    
+}
+/**
+ * Definition for singly-linked list with a random pointer.
+ * public class RandomListNode {
+ *     public int label;
+ *     public RandomListNode next, random;
+ *     public RandomListNode(int x) { this.label = x; }
+ * };
+ */