Update links in readme due to rename of main branch

Author: orfeasa

Diff for: readme.md

@@ -7,34 +7,34 @@ Each problem contains the problem description and unit tests in a separate file.
 
 ### 1. Arrays
 
-1. [Anagram Check](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-01%20Anagram%20Check)
-1. [Array pair sum](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-02%20Array%20pair%20sum)
-1. [Find the Missing Element](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-03%20Find%20the%20Missing%20Element)
-1. [Largest Continuous Sum](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-04%20Largest%20Continuous%20Sum)
-1. [Sentence Reversal](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-05%20Sentence%20Reversal)
-1. [String Compression](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-06%20String%20Compression)
-1. [Unique Characters in string](https://github.com/orfeasa/data-structure-problems/tree/master/01.%20Arrays/01-07%20Unique%20Characters%20in%20string)
+1. [Anagram Check](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-01%20Anagram%20Check)
+1. [Array pair sum](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-02%20Array%20pair%20sum)
+1. [Find the Missing Element](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-03%20Find%20the%20Missing%20Element)
+1. [Largest Continuous Sum](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-04%20Largest%20Continuous%20Sum)
+1. [Sentence Reversal](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-05%20Sentence%20Reversal)
+1. [String Compression](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-06%20String%20Compression)
+1. [Unique Characters in string](https://github.com/orfeasa/data-structure-problems/tree/main/01.%20Arrays/01-07%20Unique%20Characters%20in%20string)
 
 ### 2. Stacks, Queues and Deques
 
-1. [Implement a Stack](https://github.com/orfeasa/data-structure-problems/tree/master/02.%20Stacks%2C%20Queues%20and%20Deques/02-01%20Implement%20a%20Stack)
-1. [Implement a Queue](https://github.com/orfeasa/data-structure-problems/tree/master/02.%20Stacks%2C%20Queues%20and%20Deques/02-02%20Implement%20a%20Queue)
-1. [Implement a Deque](https://github.com/orfeasa/data-structure-problems/tree/master/02.%20Stacks%2C%20Queues%20and%20Deques/02-03%20Implement%20a%20Deque)
-1. [Balanced Parentheses Check](https://github.com/orfeasa/data-structure-problems/tree/master/02.%20Stacks%2C%20Queues%20and%20Deques/02-04%20Balanced%20Parentheses%20Check)
-1. [Implement a Queue Using Two Stacks](https://github.com/orfeasa/data-structure-problems/tree/master/02.%20Stacks%2C%20Queues%20and%20Deques/02-05%20Implement%20a%20Queue%20Using%20Two%20Stacks)
+1. [Implement a Stack](https://github.com/orfeasa/data-structure-problems/tree/main/02.%20Stacks%2C%20Queues%20and%20Deques/02-01%20Implement%20a%20Stack)
+1. [Implement a Queue](https://github.com/orfeasa/data-structure-problems/tree/main/02.%20Stacks%2C%20Queues%20and%20Deques/02-02%20Implement%20a%20Queue)
+1. [Implement a Deque](https://github.com/orfeasa/data-structure-problems/tree/main/02.%20Stacks%2C%20Queues%20and%20Deques/02-03%20Implement%20a%20Deque)
+1. [Balanced Parentheses Check](https://github.com/orfeasa/data-structure-problems/tree/main/02.%20Stacks%2C%20Queues%20and%20Deques/02-04%20Balanced%20Parentheses%20Check)
+1. [Implement a Queue Using Two Stacks](https://github.com/orfeasa/data-structure-problems/tree/main/02.%20Stacks%2C%20Queues%20and%20Deques/02-05%20Implement%20a%20Queue%20Using%20Two%20Stacks)
 
 ### 3. Linked Lists
 
-1. [Singly Linked List Cycle Check](https://github.com/orfeasa/data-structure-problems/tree/master/03.%20Linked%20Lists/03-01%20Singly%20Linked%20List%20Cycle%20Check)
-1. [Linked List Reversal](https://github.com/orfeasa/data-structure-problems/tree/master/03.%20Linked%20Lists/03-02%20Linked%20List%20Reversal)
-1. [Linked List Nth to Last Node](https://github.com/orfeasa/data-structure-problems/tree/master/03.%20Linked%20Lists/03-03%20Linked%20List%20Nth%20to%20Last%20Node)
+1. [Singly Linked List Cycle Check](https://github.com/orfeasa/data-structure-problems/tree/main/03.%20Linked%20Lists/03-01%20Singly%20Linked%20List%20Cycle%20Check)
+1. [Linked List Reversal](https://github.com/orfeasa/data-structure-problems/tree/main/03.%20Linked%20Lists/03-02%20Linked%20List%20Reversal)
+1. [Linked List Nth to Last Node](https://github.com/orfeasa/data-structure-problems/tree/main/03.%20Linked%20Lists/03-03%20Linked%20List%20Nth%20to%20Last%20Node)
 
 ### 4. Recursion
 
-1. [Word Split](https://github.com/orfeasa/data-structure-problems/tree/master/04.%20Recursion/04-01%20Word%20Split)
-1. [Reverse String](https://github.com/orfeasa/data-structure-problems/tree/master/04.%20Recursion/04-02%20Reverse%20a%20String)
-1. [String Permutation](https://github.com/orfeasa/data-structure-problems/tree/master/04.%20Recursion/04-03%20String%20Permutation)
-1. [Fibonacci Sequence](https://github.com/orfeasa/data-structure-problems/tree/master/04.%20Recursion/04-04%20Fibonacci%20Sequence)
+1. [Word Split](https://github.com/orfeasa/data-structure-problems/tree/main/04.%20Recursion/04-01%20Word%20Split)
+1. [Reverse String](https://github.com/orfeasa/data-structure-problems/tree/main/04.%20Recursion/04-02%20Reverse%20a%20String)
+1. [String Permutation](https://github.com/orfeasa/data-structure-problems/tree/main/04.%20Recursion/04-03%20String%20Permutation)
+1. [Fibonacci Sequence](https://github.com/orfeasa/data-structure-problems/tree/main/04.%20Recursion/04-04%20Fibonacci%20Sequence)
 1. Coin Change
 
 ### 5. Trees