When you dealing with sub array problems
Fast/Slow
Fast/Catch-Up
Fast/Lagging
Front/Back
Looks for Sort (Use PriorityQueue)
Two point with Sorting [Pair]
Handling Duplicates [Decoding]
Use HashMap to store the counts
If character, then user char[] ch = new char[26] to store the counts
Use stack when you need to look back the value for some interval
Ternary expression or handling "()" problems
Histogram kind of problems
For any dictionary related or sorting list of dictionary use Trie
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