Language Coverage and Conventions

Relevant source files

• solution/0000-0099/0001.Two Sum/README.md
• solution/0000-0099/0001.Two Sum/README_EN.md
• solution/0000-0099/0001.Two Sum/Solution.cpp
• solution/0000-0099/0001.Two Sum/Solution.cs
• solution/0000-0099/0001.Two Sum/Solution.go
• solution/0000-0099/0001.Two Sum/Solution.java
• solution/0000-0099/0001.Two Sum/Solution.js
• solution/0000-0099/0001.Two Sum/Solution.nim
• solution/0000-0099/0001.Two Sum/Solution.php
• solution/0000-0099/0001.Two Sum/Solution.py
• solution/0000-0099/0001.Two Sum/Solution.rb
• solution/0000-0099/0001.Two Sum/Solution.rs
• solution/0000-0099/0001.Two Sum/Solution.swift
• solution/0000-0099/0001.Two Sum/Solution.ts
• solution/0000-0099/0002.Add Two Numbers/README.md
• solution/0000-0099/0002.Add Two Numbers/README_EN.md
• solution/0000-0099/0002.Add Two Numbers/Solution.c
• solution/0000-0099/0002.Add Two Numbers/Solution.cpp
• solution/0000-0099/0002.Add Two Numbers/Solution.cs
• solution/0000-0099/0002.Add Two Numbers/Solution.go
• solution/0000-0099/0002.Add Two Numbers/Solution.java
• solution/0000-0099/0002.Add Two Numbers/Solution.js
• solution/0000-0099/0002.Add Two Numbers/Solution.nim
• solution/0000-0099/0002.Add Two Numbers/Solution.py
• solution/0000-0099/0002.Add Two Numbers/Solution.rb
• solution/0000-0099/0002.Add Two Numbers/Solution.rs
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/README.md
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/README_EN.md
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.cpp
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.cs
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.go
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.java
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.js
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.php
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.py
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.rs
• solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.ts

Purpose and Scope

This document catalogs the 10+ programming languages supported in the LeetCode solutions repository and documents the language-specific idioms, naming conventions, and coding patterns used consistently across all problem implementations. Each problem typically provides solutions in multiple languages, allowing learners to compare algorithmic implementations across different programming paradigms.

For information about automated code formatting that enforces these conventions, see Code Formatting System.

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Supported Languages Overview

The repository provides solutions in 16 programming languages, ordered by prevalence and community adoption:

Language	File Extension	Primary Use Case	Memory Management
Python3	.py	Rapid prototyping, readability	Automatic (GC)
Java	.java	Enterprise, verbose clarity	Automatic (GC)
C++	.cpp	Performance-critical, STL	Manual/RAII
Go	.go	Concurrency, simplicity	Automatic (GC)
TypeScript	.ts	Type-safe JavaScript	Automatic (GC)
Rust	.rs	Memory safety, systems	Ownership system
JavaScript	.js	Web, dynamic typing	Automatic (GC)
C#	.cs	.NET ecosystem	Automatic (GC)
PHP	.php	Web backend	Automatic (GC)
Scala	.scala	Functional/OOP hybrid	Automatic (GC)
Swift	.swift	iOS/macOS development	ARC
Ruby	.rb	Scripting, Rails	Automatic (GC)
Kotlin	.kt	Android, JVM	Automatic (GC)
Nim	.nim	Systems, Python-like syntax	Manual/GC hybrid
Cangjie	.cj	Emerging language	Automatic (GC)
C	.c	Low-level, embedded	Manual

Sources: solution/0000-0099/0001.Two Sum/README.md81-403 solution/0000-0099/0003.Longest Substring Without Repeating Characters/README.md77-328

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File Organization and Naming

Standard File Structure

Each problem directory follows a consistent naming pattern:

solution/XXXX-XXXX/<problem_id>/
├── README.md              # Chinese documentation
├── README_EN.md           # English documentation
├── Solution.py            # Python implementation
├── Solution.java          # Java implementation
├── Solution.cpp           # C++ implementation
├── Solution.go            # Go implementation
├── Solution.ts            # TypeScript implementation
├── Solution.rs            # Rust implementation
├── Solution.js            # JavaScript implementation
├── Solution.cs            # C# implementation
├── Solution.php           # PHP implementation
├── Solution.scala         # Scala implementation
├── Solution.swift         # Swift implementation
├── Solution.rb            # Ruby implementation
├── Solution.kt            # Kotlin implementation
├── Solution.nim           # Nim implementation
├── Solution.cj            # Cangjie implementation
└── Solution.c             # C implementation

Tab Organization in Documentation

README files present solutions in collapsible tabs, ordered by language popularity:

This structure appears in both Chinese (README.md79-405) and English (README_EN.md76-402) documentation.

Sources: solution/0000-0099/0001.Two Sum/README.md1-410 solution/0000-0099/0001.Two Sum/README_EN.md1-407

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Language-Specific Idioms and Patterns

Hash Table Implementation Patterns

Different languages use distinct data structures and APIs for hash-based lookups:

Example Comparison: Two Sum Hash Lookup

Language	Hash Table Type	Insertion	Lookup Pattern
Python	dict	d[x] = i	(y := target - x) in d (walrus operator)
Java	HashMap<Integer, Integer>	d.put(x, i)	d.containsKey(y) then d.get(y)
C++	unordered_map<int, int>	d[x] = i	d.contains(y) (C++20)
Go	map[int]int	d[x] = i	j, ok := d[y]; if ok
TypeScript	Map<number, number>	d.set(x, i)	d.has(y) then d.get(y)!
Rust	HashMap<i32, i32>	d.insert(x, i)	if let Some(&j) = d.get(&y)

Sources: solution/0000-0099/0001.Two Sum/Solution.py1-8 solution/0000-0099/0001.Two Sum/Solution.java1-14 solution/0000-0099/0001.Two Sum/Solution.cpp1-15 solution/0000-0099/0001.Two Sum/Solution.go1-12 solution/0000-0099/0001.Two Sum/Solution.ts1-12 solution/0000-0099/0001.Two Sum/Solution.rs1-16

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Null/Optional Handling

Handling absence of values varies dramatically across languages:

Concrete Examples from Add Two Numbers:

Language	Null Check Pattern	Value Access
Python	l1.val if l1 else 0	Conditional expression
Java	l1 == null ? 0 : l1.val	Ternary operator
C++	l1 ? l1->val : 0	Pointer truthiness
Go	if l1 != nil { s += l1.Val }	Explicit if statement
TypeScript	l1?.val || 0	Optional chaining with nullish coalescing
Rust	if let Some(node) = l1 { sum += node.val; }	Pattern matching
JavaScript	l1?.val || 0	Optional chaining
Swift	if let node = l1 { s += node.val }	Optional binding
Ruby	l1.nil? ? 0 : l1.val	nil? predicate
PHP	$l1 !== null ? $l1->val : 0	Strict comparison

Sources: solution/0000-0099/0002.Add Two Numbers/Solution.py10-18 solution/0000-0099/0002.Add Two Numbers/Solution.java17-18 solution/0000-0099/0002.Add Two Numbers/Solution.cpp18 solution/0000-0099/0002.Add Two Numbers/Solution.go14-19 solution/0000-0099/0002.Add Two Numbers/Solution.rs25-33

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Loop and Iteration Patterns

Sliding Window Loop Example (from Longest Substring):

Language	Loop Structure	Counter Management
Python	for r, c in enumerate(s):	cnt = Counter() with cnt[c] += 1
Java	for (int l = 0, r = 0; r < n; ++r)	int[] cnt = new int[128] with ++cnt[c]
C++	for (int l = 0, r = 0; r < n; ++r)	int cnt[128]{} zero-initialized
Go	for r, c := range s	cnt := [128]int{} array
TypeScript	for (let l = 0, r = 0; r < n; ++r)	const cnt = new Map<string, number>()
Rust	for (r, &c) in chars.iter().enumerate()	let mut cnt = [0; 128] array
PHP	for ($r = 0; $r < $n; ++$r)	$cnt = array_fill(0, 128, 0)

Sources: solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.py5-6 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.java5-6 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.cpp6 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.go4

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Memory Management and Ownership

Linked List Node Allocation Examples:

Language	Node Creation	Memory Model	Cleanup
Python	ListNode(val)	Reference counting + GC	Automatic
Java	new ListNode(s % 10)	Heap allocation, GC	Automatic
C++	new ListNode(s % 10)	Heap allocation	Manual (or RAII)
Go	&ListNode{s % 10, nil}	Escape analysis determines heap/stack	Automatic
Rust	Box::new(ListNode::new(sum % 10))	Heap allocation, owned	Automatic (Drop trait)
C	malloc(sizeof(struct ListNode))	Explicit heap	Explicit free()
Swift	ListNode.init(s % 10)	ARC	Automatic

Sources: solution/0000-0099/0002.Add Two Numbers/Solution.py15 solution/0000-0099/0002.Add Two Numbers/Solution.java19 solution/0000-0099/0002.Add Two Numbers/Solution.cpp20 solution/0000-0099/0002.Add Two Numbers/Solution.go20 solution/0000-0099/0002.Add Two Numbers/Solution.rs34 solution/0000-0099/0002.Add Two Numbers/Solution.c30-31

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Data Structure Conventions

Character/String Counting Arrays

Fixed-size arrays for ASCII/Unicode character counting:

Language	Declaration	Indexing	Notes
Python	cnt = Counter() or cnt = {}	cnt[c]	Uses dict for sparse data
Java	int[] cnt = new int[128];	cnt[c]	Direct char-to-int conversion
C++	int cnt[128]{};	cnt[s[r]]	Zero-initialization with {}
Go	cnt := [128]int{}	cnt[c]	Array literal
TypeScript	const cnt = new Map<string, number>()	cnt.get(s[r])	Map for Unicode safety
Rust	let mut cnt = [0; 128];	cnt[c as usize]	Explicit type cast
C	int freq[256] = {0};	freq[(unsigned char) c]	Unsigned to avoid negatives
PHP	$cnt = array_fill(0, 128, 0);	$cnt[ord($s[$r])]	ord() for ASCII value

Sources: solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.py3 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.java3 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.cpp4 solution/0000-0099/0003.Longest Substring Without Repeating Characters/Solution.go2

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Dummy Node Pattern for Linked Lists

All languages use a dummy/sentinel node to simplify list construction:

Initialization Patterns:

• Python: dummy = ListNode() - default constructor
• Java: ListNode dummy = new ListNode(0); - explicit value
• C++: ListNode dummy; (stack) or ListNode* dummy = new ListNode(0); (heap)
• Go: dummy := &ListNode{} - struct literal with address-of
• Rust: let mut dummy = Some(Box::new(ListNode::new(0))); - wrapped in Option
• C: struct ListNode* dummy = malloc(sizeof(struct ListNode)); - manual allocation
• Swift: var dummy = ListNode.init() - explicit init
• PHP: $dummy = new ListNode(0); - object instantiation

Sources: solution/0000-0099/0002.Add Two Numbers/Solution.py10 solution/0000-0099/0002.Add Two Numbers/Solution.java13 solution/0000-0099/0002.Add Two Numbers/Solution.cpp14 solution/0000-0099/0002.Add Two Numbers/Solution.go9 solution/0000-0099/0002.Add Two Numbers/Solution.rs22 solution/0000-0099/0002.Add Two Numbers/Solution.c11-13

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Language-Specific Syntax Highlights

Modern Language Features

Python: Walrus Operator and Type Hints

Source: solution/0000-0099/0001.Two Sum/Solution.py2-7

TypeScript: Non-Null Assertions and Generics

Source: solution/0000-0099/0001.Two Sum/Solution.ts1-11

Rust: Pattern Matching and Ownership

Source: solution/0000-0099/0001.Two Sum/Solution.rs1-16

C++: Contains Method (C++20)

Source: solution/0000-0099/0001.Two Sum/Solution.cpp8-9

Go: Multiple Return Values

Source: solution/0000-0099/0001.Two Sum/Solution.go6-7

Swift: Optional Binding

Source: solution/0000-0099/0001.Two Sum/Solution.swift5-7

JavaScript: Optional Chaining

Source: solution/0000-0099/0002.Add Two Numbers/Solution.js18

PHP: Isset for Array Keys

Source: solution/0000-0099/0001.Two Sum/Solution.php11-13

Ruby: Predicate Methods

Source: solution/0000-0099/0001.Two Sum/Solution.rb7-9

Nim: Functional Style

Source: solution/0000-0099/0002.Add Two Numbers/Solution.nim27-28

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Cross-Language Algorithm Equivalence

Example: Two Sum Complete Implementation

The following diagram shows how the same hash table algorithm maps to code symbols across languages:

Sources: solution/0000-0099/0001.Two Sum/Solution.py solution/0000-0099/0001.Two Sum/Solution.java solution/0000-0099/0001.Two Sum/Solution.cpp solution/0000-0099/0001.Two Sum/Solution.go solution/0000-0099/0001.Two Sum/Solution.rs

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Summary: Language Selection Guide

Choose...	When you need...	Trade-offs
Python	Rapid prototyping, readable code	Slower runtime, dynamic typing
Java	Enterprise compatibility, strong typing	Verbose syntax, boilerplate
C++	Maximum performance, STL algorithms	Complex syntax, manual memory
Go	Simplicity, concurrency	Limited generics (pre-1.18)
TypeScript	Type-safe JavaScript, IDE support	Compilation step required
Rust	Memory safety + performance	Steep learning curve, ownership
JavaScript	Web environments, dynamic	Runtime type errors, implicit coercion
C#	.NET ecosystem, Windows apps	Platform dependency
PHP	Web backends, legacy systems	Inconsistent APIs
Swift	Apple platforms, modern syntax	Platform-specific
Ruby	Scripting, metaprogramming	Slower execution
Nim	Python-like + compiled performance	Smaller ecosystem

Sources: All solution files in solution/0000-0099/0001.Two Sum/ solution/0000-0099/0002.Add Two Numbers/ solution/0000-0099/0003.Longest Substring Without Repeating Characters/