LeetCode practice covering

• Matrices
• Arrays (merging sorted arrays)
• String manipulation (longest substring, find repeated DNS sequence)
• Sliding window
• Array
• Graphs
• Tries

General guidelines

• If question is asking top/maximum/minimum/closest K elements among N elements,
  • use a Heap
• If the given input is a sorted array or list, use either a binary search or 2-pointers strategy
• If we need to try all combinations (or permutations) of the input, use either backtracking or BFS (bread-first search)
• Most questions related to Tree or Graphs can be solved either thru a BFS or DFS
• Every recursive solution can be converted to an iterative solution using a stack
• For a problem involving arrays, if there exists a solution in O(n ^ 2) time, and O(1) space, there must exist 2 other solutions -- Using a HashMap or a Set for O(n) time and O(n) space -- Using sorting for O(n log n) time and O(1) space
• If a problem is asking for optimization (e.g. maximization or minimization), use Dynamic Programming
• If we need to find some common substring among a set of string, use a HashMap or Trie
• If we need to search/manipulate a bunch of strings, a Trie will be the best data structure
• If the problem is related to a LinkedList, and we can't use extra space, then use the Fast and Slow pointer approach