randomized set

Author: jackzhenguo

HashTable/HashTable.Lib/RandomizedSet.cs

@@ -0,0 +1,80 @@
+/* ==============================================================================
+ * 功能描述：IDG  
+ * 创 建 者：gz
+ * 创建日期：2017/5/10 12:41:14
+ * ==============================================================================*/
+using System;
+using System.Collections.Generic;
+using System.Data.SqlTypes;
+using System.Linq;
+using System.Text;
+using System.Threading;
+
+namespace IDGSln
+{
+
+    /// <summary>
+    /// IDG
+    /// </summary>
+    public class RandomizedSet
+    {
+        //insert remove getRandom
+        private Dictionary<int, int> _dict;  //key: value, Value: index
+        private List<int> _valList; //element of value list, for it can get the O(1) visit
+        public RandomizedSet()
+        {
+            _dict = new Dictionary<int, int>();
+            _valList = new List<int>();
+        }
+
+        public bool Insert(int val)
+        {
+            if (!_dict.ContainsKey(val))
+            {
+                _dict.Add(val, _valList.Count);
+                _valList.Add(val);
+                return true;
+            }
+            return false;
+        }
+
+        public bool Remove(int val)
+        {
+            if (!_dict.ContainsKey(val)) return false;
+            int removeIndex = _dict[val]; //_dict.Values: element index collection
+
+            swapToLast(removeIndex);
+
+            _valList.Remove(val);
+            _dict.Remove(val);
+            return true;
+        }
+
+        //i-待移除元素的索引
+        //将待移除元素移到_valList的末尾，修改原来末尾元素在字典中的键值
+        private void swapToLast(int i)
+        {
+            int lastIndex = _valList.Count - 1;
+            if (i > lastIndex) return;
+            int lastVal = _valList[lastIndex];
+            int tmpVal = _valList[i];
+            _valList[i] = lastVal; // the key is to prove " i < lastIndex" !!!
+            _valList[lastIndex] = tmpVal;
+            //this is important, to update the last index value in dictionary
+            _dict[lastVal] = i; 
+        }
+
+        public int GetRandom()
+        {
+            long tick = DateTime.Now.Ticks;
+            Random ran = new Random((int)(tick & 0xffffffffL) | (int)(tick >> 32));
+            int randnum = ran.Next(_valList.Count);
+            if (_valList.Count == 0) return -1;
+            Thread.Sleep(20);
+
+            return _valList[randnum];
+        }
+
+    }
+
+}