LeetCode Java Solutions

     

Hi 👋, I'm Chee Hwa and welcome to LeetCode Solutions in Java.

As I'm new to LeetCode and programming in general, I'm practicing everyday and hope to share my solutions and learnings with you.

• Exclusively on Java
• Beginner problems
• Daily Challenge if within my ability

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Latest Solutions

Date	Problem	Difficulty	Solution	Topics
November 8th	1544. Make The String Great	$\text{\color{TealBlue}Easy}$	Stack	Stack, String
November 7th	1323. Maximum 69 Number	$\text{\color{TealBlue}Easy}$	Math or String	Greedy, Math
November 6th	2136. Earliest Possible Day of Full Bloom	$\text{\color{Red}Hard}$	Sorting	Array, Greedy, Sorting
November 5th	2131. Longest Palindrome by Concatenating Two Letter Words	$\text{\color{Dandelion}Medium}$	Counting or Hash Table	Array, Counting, Greedy, Hash Table, String
November 4th	345. Reverse Vowels of a String	$\text{\color{TealBlue}Easy}$	Two Pointers	String, Two Pointers

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Topics

The problem sets and solutions are grouped into Topics as stated in LeetCode.

• Array
• Backtracking
• Binary Search
• Bit Manipulation
• Counting
• Dynamic Programming
• Enumeration
• Geometry
• Greedy
• Hash Table
• Heap (Priority Queue)
• Math
• Matrix
• Number Theory
• Prefix Sum
• Simulation
• Sorting
• Stack
• String
• Two Pointers

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Array

#	Problem	Solution	Difficulty	Topics	Note
1	Two Sum	Java	$\text{\color{TealBlue}Easy}$	Array, Hash Table
49	Group Anagrams	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, String
238	Product of Array Except Self	Java	$\text{\color{Dandelion}Medium}$	Array, Prefix Sum
334	Increasing Triplet Subsequence	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy
368	Largest Divisible Subset	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Math, Sorting
393	UTF-8 Validation	Java without or with Bit Manipulation	$\text{\color{Dandelion}Medium}$	Array, Bit Manipulation
485	Maximum Consecutive Ones	Java	$\text{\color{TealBlue}Easy}$	Array
523	Continuous Subarray Sum	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Math, Prefix Sum
560	Subarray Sum Equals K	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Prefix Sum
609	Find Duplicate File in System	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, String
645	Set Mismatch	Java with Bit Manipulation, Hash Table or Sorting	$\text{\color{TealBlue}Easy}$	Array, Bit Manipulation, Hash Table, Sorting
766	Toeplitz Matrix	Java	$\text{\color{TealBlue}Easy}$	Array, Matrix	Follow up: One Row at a Time and One Column at a Time
812	Largest Triangle Area	Java	$\text{\color{TealBlue}Easy}$	Array, Geometry, Math
835	Image Overlap	Java with Bit Manipulation or Hash Table	$\text{\color{Dandelion}Medium}$	Array, Matrix
929	Unique Email Addresses	Java	$\text{\color{TealBlue}Easy}$	Array, Hash Table, String
948	Bag of Tokens	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy, Sorting, Two Pointers
976	Largest Perimeter Triangle	Java	$\text{\color{TealBlue}Easy}$	Array, Greedy, Math, Sorting
985	Sum of Even Numbers After Queries	Java	$\text{\color{Dandelion}Medium}$	Array, Simulation
1239	Maximum Length of a Concatenated String with Unique Characters	Java with Backtracking or Bit Manipulation	$\text{\color{Dandelion}Medium}$	Array, Backtracking, Bit Manipulation, String
1337	The K Weakest Rows in a Matrix	Java with Heap (Priority Queue) or Sorting	$\text{\color{TealBlue}Easy}$	Array, Binary Search, Heap (Priority Queue), Matrix, Sorting
1480	Running Sum of 1D Array	Java	$\text{\color{TealBlue}Easy}$	Array, Prefix Sum
1578	Minimum Time to Make Rope Colorful	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Greedy, String
1672	Richest Customer Wealth	Java	$\text{\color{TealBlue}Easy}$	Array, Matrix
1679	Max Number of K-Sum Pairs	Java with Hash Table or Sorting & Two Pointers	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, Two Pointers
1711	Count Good Meals	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table
1979	Find Greatest Common Divisor of Array	Java	$\text{\color{TealBlue}Easy}$	Array, Math, Number Theory
1995	Count Special Quadruplets	Java	$\text{\color{TealBlue}Easy}$	Array, Enumeration	Solution Using Hash Table
2007	Find Original Array From Doubled Array	Java with Hash Table, Queue or Counting Array	$\text{\color{Dandelion}Medium}$	Array, Greedy, Hash Table, Sorting
2131	Longest Palindrome by Concatenating Two Letter Words	Java with Counting or Hash Table	$\text{\color{Dandelion}Medium}$	Array, Counting, Greedy, Hash Table, String
2136	Earliest Possible Day of Full Bloom	Java	$\text{\color{Red}Hard}$	Array, Greedy, Sorting
2176	Count Equal and Divisible Pairs in an Array	Java	$\text{\color{TealBlue}Easy}$	Array
2438	Range Product Queries of Powers	Java	$\text{\color{Dandelion}Medium}$	Array, Bit Manipulation, Prefix Sum

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Backtracking

#	Problem	Solution	Difficulty	Topics	Note
1239	Maximum Length of a Concatenated String with Unique Characters	Java	$\text{\color{Dandelion}Medium}$	Array, Backtracking, Bit Manipulation, String	Solution Using Bit Manipulation

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Binary Search

#	Problem	Solution	Difficulty	Topics	Note
1337	The K Weakest Rows in a Matrix	Java with Heap (Priority Queue) or Sorting	$\text{\color{TealBlue}Easy}$	Array, Binary Search, Heap (Priority Queue), Matrix, Sorting	Solution Using Linear Search

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Bit Manipulation

#	Problem	Solution	Difficulty	Topics	Note
29	Divide Two Integers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math
371	Sum of Two Integers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math
393	UTF-8 Validation	Java	$\text{\color{Dandelion}Medium}$	Array, Bit Manipulation
645	Set Mismatch	Java	$\text{\color{TealBlue}Easy}$	Array, Bit Manipulation, Hash Table, Sorting	Solution Using Hash Table or Sorting
1239	Maximum Length of a Concatenated String with Unique Characters	Java	$\text{\color{Dandelion}Medium}$	Array, Backtracking, Bit Manipulation, String	Solution Using Backtracking
1342	Number of Steps to Reduce a Number to Zero	Java	$\text{\color{TealBlue}Easy}$	Bit Manipulation, Math	Solution Using Math
1486	XOR Operation in an Array	Java	$\text{\color{TealBlue}Easy}$	Bit Manipulation, Math
1680	Concatenation of Consecutive Binary Numbers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math, Simulation	Solution Using Math
2438	Range Product Queries of Powers	Java	$\text{\color{Dandelion}Medium}$	Array, Bit Manipulation, Prefix Sum

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Counting

#	Problem	Solution	Difficulty	Topics	Note
383	Ransom Note	Java	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String	Solution Using Hash Table
2131	Longest Palindrome by Concatenating Two Letter Words	Java	$\text{\color{Dandelion}Medium}$	Array, Counting, Greedy, Hash Table, String	Solution Using Hash Table
2351	First Letter to Appear Twice	Java	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String	Solution Using Hash Table

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Dynamic Programming

#	Problem	Solution	Difficulty	Topics	Note
368	Largest Divisible Subset	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Math, Sorting
1578	Minimum Time to Make Rope Colorful	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Greedy, String

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Enumeration

#	Problem	Solution	Difficulty	Topics	Note
1995	Count Special Quadruplets	Java	$\text{\color{TealBlue}Easy}$	Array, Enumeration	Solution Using Hash Table
2240	Number of Ways to Buy Pens and Pencils	Java	$\text{\color{Dandelion}Medium}$	Enumeration, Math
2437	Number of Valid Clock Times	Java	$\text{\color{TealBlue}Easy}$	Enumeration, String

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Geometry

#	Problem	Solution	Difficulty	Topics	Note
593	Valid Square	Java	$\text{\color{Dandelion}Medium}$	Geometry, Math
812	Largest Triangle Area	Java	$\text{\color{TealBlue}Easy}$	Array, Geometry, Math

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Greedy

#	Problem	Solution	Difficulty	Topics	Note
334	Increasing Triplet Subsequence	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy
948	Bag of Tokens	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy, Sorting, Two Pointers
976	Largest Perimeter Triangle	Java	$\text{\color{TealBlue}Easy}$	Array, Greedy, Math, Sorting
1323	Maximum 69 Number	Java with Math or String	$\text{\color{TealBlue}Easy}$	Greedy, Math
1328	Break a Palindrome	Java	$\text{\color{Dandelion}Medium}$	Greedy, String
1578	Minimum Time to Make Rope Colorful	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Greedy, String
2007	Find Original Array From Doubled Array	Java with Hash Table, Queue or Counting Array	$\text{\color{Dandelion}Medium}$	Array, Greedy, Hash Table, Sorting
2131	Longest Palindrome by Concatenating Two Letter Words	Java with Counting or Hash Table	$\text{\color{Dandelion}Medium}$	Array, Counting, Greedy, Hash Table, String
2136	Earliest Possible Day of Full Bloom	Java	$\text{\color{Red}Hard}$	Array, Greedy, Sorting

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Hash Table

#	Problem	Solution	Difficulty	Topics	Note
1	Two Sum	Java	$\text{\color{TealBlue}Easy}$	Array, Hash Table
12	Integer to Roman	Java	$\text{\color{Dandelion}Medium}$	Hash Table, Math, String
13	Roman to Integer	Java	$\text{\color{TealBlue}Easy}$	Hash Table, Math, String	Solution Without Hash Table
49	Group Anagrams	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, String
383	Ransom Note	Java	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String	Solution Using Counting Array
523	Continuous Subarray Sum	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Math, Prefix Sum
560	Subarray Sum Equals K	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Prefix Sum
609	Find Duplicate File in System	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, String
645	Set Mismatch	Java	$\text{\color{TealBlue}Easy}$	Array, Bit Manipulation, Hash Table, Sorting	Solution Using Bit Manipulation or Sorting
929	Unique Email Addresses	Java	$\text{\color{TealBlue}Easy}$	Array, Hash Table, String
1679	Max Number of K-Sum Pairs	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, Two Pointers	Solution Using Sorting & Two Pointers
1711	Count Good Meals	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table
1832	Check if the Sentence is Pangram	Java	$\text{\color{TealBlue}Easy}$	Hash Table, String	Solution Without Hash Table
1935	Maximum Number of Words You Can Type	Java	$\text{\color{TealBlue}Easy}$	Hash Table, String
2007	Find Original Array From Doubled Array	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy, Hash Table, Sorting	Solution Using Queue or Counting Array
2131	Longest Palindrome by Concatenating Two Letter Words	Java	$\text{\color{Dandelion}Medium}$	Array, Counting, Greedy, Hash Table, String	Solution Using Counting
2351	First Letter to Appear Twice	Java	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String	Solution Using Counting

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Heap (Priority Queue)

#	Problem	Solution	Difficulty	Topics	Note
1337	The K Weakest Rows in a Matrix	Java	$\text{\color{TealBlue}Easy}$	Array, Binary Search, Heap (Priority Queue), Matrix, Sorting	Solution Using Sorting

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Math

#	Problem	Solution	Difficulty	Topics	Note
12	Integer to Roman	Java	$\text{\color{Dandelion}Medium}$	Hash Table, Math, String
13	Roman to Integer	Java	$\text{\color{TealBlue}Easy}$	Hash Table, Math, String	Solution Using Hash Table
29	Divide Two Integers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math
368	Largest Divisible Subset	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Math, Sorting
371	Sum of Two Integers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math
412	Fizz Buzz	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation, String
523	Continuous Subarray Sum	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Math, Prefix Sum
593	Valid Square	Java	$\text{\color{Dandelion}Medium}$	Geometry, Math
812	Largest Triangle Area	Java	$\text{\color{TealBlue}Easy}$	Array, Geometry, Math
976	Largest Perimeter Triangle	Java	$\text{\color{TealBlue}Easy}$	Array, Greedy, Math, Sorting
1071	Greatest Common Divisor of Strings	Java	$\text{\color{TealBlue}Easy}$	Math, String
1103	Distribute Candies to People	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation
1154	Day of the Year	Java	$\text{\color{TealBlue}Easy}$	Math, String
1323	Maximum 69 Number	Java	$\text{\color{TealBlue}Easy}$	Greedy, Math	Solution Using String
1342	Number of Steps to Reduce a Number to Zero	Java	$\text{\color{TealBlue}Easy}$	Bit Manipulation, Math	Solution Using Bit Manipulation
1486	XOR Operation in an Array	Java	$\text{\color{TealBlue}Easy}$	Bit Manipulation, Math
1680	Concatenation of Consecutive Binary Numbers	Java	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math, Simulation	Solution Using Bit Manipulation
1979	Find Greatest Common Divisor of Array	Java	$\text{\color{TealBlue}Easy}$	Array, Math, Number Theory
2169	Count Operations to Obtain Zero	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation
2240	Number of Ways to Buy Pens and Pencils	Java	$\text{\color{Dandelion}Medium}$	Enumeration, Math
2413	Smallest Even Multiple	Java	$\text{\color{TealBlue}Easy}$	Math, Number Theory

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Matrix

#	Problem	Solution	Difficulty	Topics	Note
766	Toeplitz Matrix	Java	$\text{\color{TealBlue}Easy}$	Array, Matrix	Follow up: One Row at a Time and One Column at a Time
835	Image Overlap	Java with Bit Manipulation or Hash Table	$\text{\color{Dandelion}Medium}$	Array, Matrix
1337	The K Weakest Rows in a Matrix	Java with Heap (Priority Queue) or Sorting	$\text{\color{TealBlue}Easy}$	Array, Binary Search, Heap (Priority Queue), Matrix, Sorting
1672	Richest Customer Wealth	Java	$\text{\color{TealBlue}Easy}$	Array, Matrix

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Number Theory

#	Problem	Solution	Difficulty	Topics	Note
1979	Find Greatest Common Divisor of Array	Java	$\text{\color{TealBlue}Easy}$	Array, Math, Number Theory
2413	Smallest Even Multiple	Java	$\text{\color{TealBlue}Easy}$	Math, Number Theory

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Prefix Sum

#	Problem	Solution	Difficulty	Topics	Note
238	Product of Array Except Self	Java	$\text{\color{Dandelion}Medium}$	Array, Prefix Sum
523	Continuous Subarray Sum	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Math, Prefix Sum
560	Subarray Sum Equals K	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Prefix Sum
1480	Running Sum of 1D Array	Java	$\text{\color{TealBlue}Easy}$	Array, Prefix Sum
2438	Range Product Queries of Powers	Java	$\text{\color{Dandelion}Medium}$	Array, Bit Manipulation, Prefix Sum

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Simulation

#	Problem	Solution	Difficulty	Topics	Note
412	Fizz Buzz	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation, String
985	Sum of Even Numbers After Queries	Java	$\text{\color{Dandelion}Medium}$	Array, Simulation
1103	Distribute Candies to People	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation
1680	Concatenation of Consecutive Binary Numbers	Java with Bit Manipulation or Math	$\text{\color{Dandelion}Medium}$	Bit Manipulation, Math, Simulation
2169	Count Operations to Obtain Zero	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation

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Sorting

#	Problem	Solution	Difficulty	Topics	Note
49	Group Anagrams	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, String
645	Set Mismatch	Java	$\text{\color{TealBlue}Easy}$	Array, Bit Manipulation, Hash Table, Sorting	Solution Using Bit Manipulation or Hash Table
948	Bag of Tokens	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy, Sorting, Two Pointers
976	Largest Perimeter Triangle	Java	$\text{\color{TealBlue}Easy}$	Array, Greedy, Math, Sorting
1337	The K Weakest Rows in a Matrix	Java	$\text{\color{TealBlue}Easy}$	Array, Binary Search, Heap (Priority Queue), Matrix, Sorting	Solution Using Heap (Priority Queue)
1679	Max Number of K-Sum Pairs	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, Two Pointers	Solution Using Hash Table
2007	Find Original Array From Doubled Array	Java with Hash Table or Queue	$\text{\color{Dandelion}Medium}$	Array, Greedy, Hash Table, Sorting	Solution Using Counting Array
2136	Earliest Possible Day of Full Bloom	Java	$\text{\color{Red}Hard}$	Array, Greedy, Sorting

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Stack

#	Problem	Solution	Difficulty	Topics	Note
1544	Make The String Great	Java	$\text{\color{TealBlue}Easy}$	Stack, String

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String

#	Problem	Solution	Difficulty	Topics	Note
12	Integer to Roman	Java	$\text{\color{Dandelion}Medium}$	Hash Table, Math, String
13	Roman to Integer	Java	$\text{\color{TealBlue}Easy}$	Hash Table, Math, String	Solution Using Hash Table
38	Count and Say	Java with Iterative or Recursive Algorithms	$\text{\color{Dandelion}Medium}$	String
49	Group Anagrams	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, String
151	Reverse Words in a String	Java with String or Collections Implementations	$\text{\color{Dandelion}Medium}$	String, Two Pointers	Solution Using Two Pointers
344	Reverse String	Java	$\text{\color{TealBlue}Easy}$	String, Two Pointers
345	Reverse Vowels of a String	Java	$\text{\color{TealBlue}Easy}$	String, Two Pointers
368	Largest Divisible Subset	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Math, Sorting
383	Ransom Note	Java with Counting Array or Hash Table	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String
412	Fizz Buzz	Java	$\text{\color{TealBlue}Easy}$	Math, Simulation, String
609	Find Duplicate File in System	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, String
929	Unique Email Addresses	Java	$\text{\color{TealBlue}Easy}$	Array, Hash Table, String
1071	Greatest Common Divisor of Strings	Java	$\text{\color{TealBlue}Easy}$	Math, String
1154	Day of the Year	Java	$\text{\color{TealBlue}Easy}$	Math, String
1239	Maximum Length of a Concatenated String with Unique Characters	Java with Backtracking or Bit Manipulation	$\text{\color{Dandelion}Medium}$	Array, Backtracking, Bit Manipulation, String
1328	Break a Palindrome	Java	$\text{\color{Dandelion}Medium}$	Greedy, String
1544	Make The String Great	Java	$\text{\color{TealBlue}Easy}$	Stack, String
1578	Minimum Time to Make Rope Colorful	Java	$\text{\color{Dandelion}Medium}$	Array, Dynamic Programming, Greedy, String
1592	Rearrange Spaces Between Words	Java	$\text{\color{TealBlue}Easy}$	String
1832	Check if the Sentence is Pangram	Java	$\text{\color{TealBlue}Easy}$	Hash Table, String	Solution Using Hash Table
1935	Maximum Number of Words You Can Type	Java	$\text{\color{TealBlue}Easy}$	Hash Table, String
2131	Longest Palindrome by Concatenating Two Letter Words	Java with Counting or Hash Table	$\text{\color{Dandelion}Medium}$	Array, Counting, Greedy, Hash Table, String
2315	Count Asterisks	Java	$\text{\color{TealBlue}Easy}$	String
2351	First Letter to Appear Twice	Java with Counting or Hash Table	$\text{\color{TealBlue}Easy}$	Counting, Hash Table, String
2437	Number of Valid Clock Times	Java	$\text{\color{TealBlue}Easy}$	Enumeration, String

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Two Pointers

#	Problem	Solution	Difficulty	Topics	Note
151	Reverse Words in a String	Java	$\text{\color{Dandelion}Medium}$	String, Two Pointers	Solution Using Collections
344	Reverse String	Java	$\text{\color{TealBlue}Easy}$	String, Two Pointers
345	Reverse Vowels of a String	Java	$\text{\color{TealBlue}Easy}$	String, Two Pointers
948	Bag of Tokens	Java	$\text{\color{Dandelion}Medium}$	Array, Greedy, Sorting, Two Pointers
1679	Max Number of K-Sum Pairs	Java	$\text{\color{Dandelion}Medium}$	Array, Hash Table, Sorting, Two Pointers	Solution Using Hash Table

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