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Fix aalhour#137 and aalhour#139 issues. Update skipList logic
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@Gutsonok
Gutsonok committed Aug 8, 2020
1 parent a9ce311 commit 80694da
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Showing 2 changed files with 139 additions and 52 deletions.
72 changes: 38 additions & 34 deletions DataStructures/Lists/SkipList.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -37,9 +37,6 @@ public SkipList()
_currentMaxLevel = 1;
_randomizer = new Random();
_firstNode = new SkipListNode<T>(default(T), MaxLevel);

for (int i = 0; i < MaxLevel; ++i)
_firstNode.Forwards[i] = _firstNode;
}


Expand Down Expand Up @@ -98,36 +95,43 @@ public void Add(T item)
var current = _firstNode;
var toBeUpdated = new SkipListNode<T>[MaxLevel];

// Get nodes for updated
for (int i = _currentMaxLevel - 1; i >= 0; --i)
{
while (current.Forwards[i] != _firstNode && current.Forwards[i].Value.IsLessThan(item))
while (current.Forwards[i] != null && current.Forwards[i].Value.IsLessThan(item))
{
current = current.Forwards[i];
}

toBeUpdated[i] = current;
}

// Get the next node level, and update list level if required.
int lvl = _getNextLevel();
if (lvl > _currentMaxLevel)
// Desired position to insert key
current = current.Forwards[0];

if(current == null || !current.Value.Equals(item))
{
for (int i = _currentMaxLevel; i < lvl; ++i)
toBeUpdated[i] = _firstNode;
// Get the next node level, and update list level if required.
int lvl = _getNextLevel();
if (lvl > _currentMaxLevel)
{
for (int i = _currentMaxLevel; i < lvl; ++i)
toBeUpdated[i] = _firstNode;

_currentMaxLevel = lvl;
}
_currentMaxLevel = lvl;
}

// New node
var newNode = new SkipListNode<T>(item, lvl);
var newNode = new SkipListNode<T>(item, lvl);

// Insert the new node into the skip list
for (int i = 0; i < lvl; ++i)
{
newNode.Forwards[i] = toBeUpdated[i].Forwards[i];
toBeUpdated[i].Forwards[i] = newNode;
}
// Insert the new node into the skip list
for (int i = 0; i < lvl; ++i)
{
newNode.Forwards[i] = toBeUpdated[i].Forwards[i];
toBeUpdated[i].Forwards[i] = newNode;
}

// Increment the count
++_count;
++_count;
}
}

/// <summary>
Expand All @@ -151,7 +155,7 @@ public bool Remove(T item, out T deleted)
// Mark all nodes as toBeUpdated.
for (int i = _currentMaxLevel - 1; i >= 0; --i)
{
while (current.Forwards[i] != _firstNode && current.Forwards[i].Value.IsLessThan(item))
while (current.Forwards[i] != null && current.Forwards[i].Value.IsLessThan(item))
current = current.Forwards[i];

toBeUpdated[i] = current;
Expand All @@ -160,7 +164,7 @@ public bool Remove(T item, out T deleted)
current = current.Forwards[0];

// Return default value of T if the item was not found
if (current.Value.IsEqualTo(item) == false)
if (current == null || current.Value.IsEqualTo(item) == false)
{
deleted = default(T);
return false;
Expand All @@ -170,18 +174,20 @@ public bool Remove(T item, out T deleted)
// Unlink it from the levels where it exists.
for (int i = 0; i < _currentMaxLevel; ++i)
{
if (toBeUpdated[i].Forwards[i] == current)
if (toBeUpdated[i].Forwards[i] != current)
{
toBeUpdated[i].Forwards[i] = current.Forwards[i];
break;
}

toBeUpdated[i].Forwards[i] = current.Forwards[i];
}

// Decrement the count
--_count;

// Check to see if we've deleted the highest-level node
// Decrement level
while (_currentMaxLevel > 1 && _firstNode.Forwards[_currentMaxLevel - 1] == _firstNode)
while (_currentMaxLevel > 1 && _firstNode.Forwards[_currentMaxLevel - 1] == null)
--_currentMaxLevel;

// Assign the deleted output parameter to the node.Value
Expand All @@ -194,8 +200,7 @@ public bool Remove(T item, out T deleted)
/// </summary>
public bool Contains(T item)
{
T itemOut;
return Find(item, out itemOut);
return Find(item, out var _);
}

/// <summary>
Expand All @@ -207,13 +212,13 @@ public bool Find(T item, out T result)

// Walk after all the nodes that have values less than the node we are looking for
for (int i = _currentMaxLevel - 1; i >= 0; --i)
while (current.Forwards[i] != _firstNode && current.Forwards[i].Value.IsLessThan(item))
while (current.Forwards[i] != null && current.Forwards[i].Value.IsLessThan(item))
current = current.Forwards[i];

current = current.Forwards[0];

// Return true if we found the element; false otherwise
if (current.Value.IsEqualTo(item))
if (current != null && current.Value.IsEqualTo(item))
{
result = current.Value;
return true;
Expand Down Expand Up @@ -290,7 +295,7 @@ public bool TryPeek(out T result)
public IEnumerator<T> GetEnumerator()
{
var node = _firstNode;
while (node.Forwards[0] != null && node.Forwards[0] != _firstNode)
while (node.Forwards[0] != null && node.Forwards[0] != null)
{
node = node.Forwards[0];
yield return node.Value;
Expand Down Expand Up @@ -349,9 +354,6 @@ public void Clear()
_currentMaxLevel = 1;
_randomizer = new Random();
_firstNode = new SkipListNode<T>(default(T), MaxLevel);

for (int i = 0; i < MaxLevel; ++i)
_firstNode.Forwards[i] = _firstNode;
}
#endregion

Expand All @@ -364,7 +366,9 @@ private int _getNextLevel()
int lvl = 1;

while (_randomizer.NextDouble() < Probability && lvl <= _currentMaxLevel && lvl < MaxLevel)
{
++lvl;
}

return lvl;
}
Expand Down
119 changes: 101 additions & 18 deletions UnitTest/DataStructuresTests/SkipListTest.cs
View file
Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
using System.Collections.Generic;
using System.Runtime.InteropServices.ComTypes;
using DataStructures.Lists;
using Xunit;

Expand All @@ -7,51 +7,128 @@ namespace UnitTest.DataStructuresTests
public static class SkipListTest
{
[Fact]
public static void AddOneElement()
public static void Initialization_ListIsEmpty()
{
var skipList = new SkipList<int>();

Assert.True(skipList.Count == 0);
Assert.True(skipList.IsEmpty);
Assert.DoesNotContain(0, skipList);
}

[Fact]
public static void Add_NullElement_ListContainNullElement()
{
var skipList = new SkipList<string>();

skipList.Add(null);

Assert.True(skipList.Count == 1);
Assert.Contains(null, skipList);
}

[Theory]
[InlineData(10)]
[InlineData(-10)]
public static void Add_OneElement_ListContainOneElement(int testValue)
{
var skipList = new SkipList<int>();

skipList.Add(testValue);

Assert.True(skipList.Count == 1);
Assert.Contains(testValue, skipList);
}

[Fact]
public static void Add_OneElementTwice_ListContainOneElement()
{
var skipList = new SkipList<int>();

skipList.Add(10);
skipList.Add(10);

Assert.True(skipList.Count == 1);
Assert.Contains(10, skipList);
}

[Fact]
public static void AddBatchOfElements()
public static void Add_DefaultElement_ListContainOneElement()
{
var skipList = new SkipList<int>();

for (int i = 100; i > 50; --i)
{
skipList.Add(i);
}
skipList.Add(default(int));

Assert.True(skipList.Count == 50);
for (int i = 100; i > 50; --i)
Assert.True(skipList.Count == 1);
Assert.Contains(0, skipList);
}

[Fact]
public static void Add_SomeElements_ListContainTheseElements()
{
var skipList = new SkipList<int>();
skipList.Add(0);
skipList.Add(-1);
skipList.Add(1);
skipList.Add(2);

Assert.True(skipList.Count == 4);
int checkValue = -1;
foreach(var item in skipList)
{
Assert.Contains(i, skipList);
Assert.Equal(checkValue, item);
checkValue++;
}
}

[Fact]
public static void AddThreeElementsRemoveOneElement()
public static void Remove_RemoveOneElement_ListIsEmpty()
{
var skipList = new SkipList<int>();
skipList.Add(-10);

skipList.Add(1);
skipList.Remove(-10);

Assert.True(skipList.Count == 0);
Assert.DoesNotContain(0, skipList);
Assert.DoesNotContain(-10, skipList);
}

[Fact]
public static void Remove_RemoveDefaultElement_DoNoRemoveAndListIsEmptyAndAddingIsWork()
{
var skipList = new SkipList<int>();

Assert.DoesNotContain(0, skipList);
skipList.Remove(default(int));

Assert.True(skipList.Count == 0);
Assert.DoesNotContain(0, skipList);

skipList.Add(10);
Assert.True(skipList.Count == 1);
Assert.Contains(10, skipList);
}

[Fact]
public static void Remove_RemoveSomeElements_ListContainOneElement()
{
var skipList = new SkipList<int>();
skipList.Add(0);
skipList.Add(-1);
skipList.Add(2);
skipList.Add(3);

skipList.Remove(2);
skipList.Remove(-1);
skipList.Remove(3);

Assert.True(skipList.Count == 2);
Assert.Contains(1, skipList);
Assert.Contains(3, skipList);
Assert.DoesNotContain(2, skipList);
Assert.True(skipList.Count == 1);
Assert.Contains(0, skipList);
}

[Fact]
public static void AddAndRemoveBatchOfElements()
public static void AddAndRemove_BatchOfElements_ListIsEmpty()
{
var skipList = new SkipList<int>();

Expand All @@ -60,16 +137,22 @@ public static void AddAndRemoveBatchOfElements()
skipList.Add(i);
}

Assert.True(skipList.Count == 50);
for (int i = 100; i > 50; --i)
{
Assert.Contains(i, skipList);
}

for (int i = 100; i > 50; --i)
{
skipList.Remove(i);
}

Assert.True(skipList.Count == 0);
for (int i = 100; i > 50; --i)
{
Assert.DoesNotContain(i, skipList);
}
Assert.True(skipList.Count == 0);
}

[Fact]
Expand Down

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