updated README

Author: dampdigits

README.md

@@ -1,8 +1,34 @@
 # Leetcode75
 - Ace Coding Interview with 75 Qs
 - 75 essential & trending problems
+- 22 different topics
 - Must do problem list for interview prep
 
+### Topics
+1. Array / String   (9 problems)
+2. Two Pointers     (4 problems)
+3. Sliding Window   (4 problems)
+4. Prefix Sum       (2 problems)
+5. Hash Map / Set   (4 problems)
+6. Stack    (3 problems)
+7. Queue    (2 problems)
+8. Linked List          (4 problems)
+9. Binary Tree - DFS    (6 problems)
+10. Binary Tree - BFS   (2 problems)
+11. Binary Search Tree  (2 problems)
+12. Graph - DFS     (4 problems)
+13. Graph - BFS     (2 problems)
+14. Heap / Priority Queue   (4 problems)
+15. Binary Search   (4 problems)
+16. Backtracking    (2 problems)
+17. DP - 1D                 (4 problems)
+18. DP - Multidimensional   (4 problems)
+19. Bit Manipulation        (3 problems)
+20. Trie            (2 problems)
+21. Intervals       (2 problems)
+22. Monotonic Stack (2 problems)
+
+
 ### Language used in solutions
 - Java
 - Python3