118 lines
2.9 KiB
C++
118 lines
2.9 KiB
C++
// Copyright Epic Games, Inc. All Rights Reserved.
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#pragma once
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#include "Containers/Array.h"
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#include "Containers/StringView.h"
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#include "Containers/UnrealString.h"
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#include "Misc/StringBuilder.h"
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/**
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* A string prefix tree is conceptually similar to a trie.
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* However, instead of adding a new nodes per single character, nodes encode a string prefix, and entries are built up by concatenating the path to the node.
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* For example, if we add the entries "ABC", "AC", and "D" to the tree, we will have:
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* <root>
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* |- "A"
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* | |- "B"
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* | | |- "C" *
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* | |- "C" *
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* |- "D" *
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*
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* Where only the nodes marked with * are leaf nodes.
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* An entry is considered to be in the list only if it is a leaf node.
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* This tree structure allows for long strings that may have long similar sections to be searched far faster than storing them in eg. a set.
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*/
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class FStringPrefixTree
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{
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public:
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FStringPrefixTree() = default;
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~FStringPrefixTree();
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/**
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* Insert the given string into the tree.
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*/
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void Insert(FStringView ToAdd);
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/**
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* Insert all the strings in the array.
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*/
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void InsertAll(const TArray<FString>& Array);
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/**
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* Insert all the strings in the array.
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*/
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void InsertAll(const TArray<FStringView>& Array);
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/**
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* Remove an entry. This can fragment the tree and should be avoided.
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*/
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void Remove(FStringView ToRemove);
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/**
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* Clear the tree.
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*/
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void Clear();
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/**
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* Does the tree contain the given entry?
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*/
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bool Contains(FStringView Entry) const;
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/**
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* Does any entry start with the given prefix.
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* Eg. if the tree contains "Foobar", this would return true if given "Foo".
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*/
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bool AnyStartsWith(FStringView Prefix) const;
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/**
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* Returns the number of leaf entries in the tree.
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* Equivalent to the number of items added via Insert() or InsertAll().
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*/
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int32 Size() const;
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/**
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* Dump all leaf nodes into an array.
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*/
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TArray<FString> GetAllEntries() const;
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/**
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* For testing and debugging.
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* The number of internal nodes. This is a different (usually larger) number than the number of entries.
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*/
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int32 NumNodes() const;
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/**
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* For testing and debugging.
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* Pretty prints the internal tree structure as a string.
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*/
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FString DumpToString() const;
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private:
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struct FNode
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{
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FString Prefix;
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TArray<FNode> Children;
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bool IsLeaf = false;
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FNode() = default;
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~FNode();
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void Insert(FStringView ToAdd);
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void Remove(FStringView ToRemove);
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bool Contains(FStringView ToFind) const;
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bool AnyStartsWith(FStringView ToFind) const;
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int32 Size() const;
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int32 NumNodes() const;
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void GetAllEntries(const FString& CurrentPrefix, TArray<FString>& OutEntries) const;
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void DumpToString(FStringBuilderBase& Builder, TArray<bool, TInlineAllocator<32>>& DrawLines, bool bLastChild) const;
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private:
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// we can prune any node that is not a leaf and does not contain any children which are leaves anymore
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bool CanPrune() const;
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};
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FNode Root;
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}; |