Everything before this week trained execution: given the pattern, write the code. This week trains recognition: given a bare problem, name the pattern. That is the skill interviews actually test, and it is the one most people never practise on purpose.

The five-minute protocol

Frequency count: cnt[x] = cnt.get(x, 0) + 1 . Compare two counts to test anagrams; find the first key with count 1; check that one count is \"covered\" by another.
Seen set: add as you go, and act the first time you see a repeat.
Mapping consistency: map a\u2192b and b\u2192a at the same time to check a one-to-one correspondence (isomorphic strings, word patterns).

Read the problem twice. Write down the input type, the output type, and the constraints (n ≤ 10⁵ rules out O(n²)).
List the tells you notice: sorted? contiguous? "all combinations"? "shortest"? "number of ways"? dependencies? top-k?
Name one or two candidate patterns. Say why the constraints allow them.
Sketch the state you would keep (window state, DP state, stack contents) before writing any code.
Only then implement — from your own template of that week.

Quick tell-to-pattern index

Tell	First thing to try
Sorted, pairs, in-place	Two pointers
Contiguous subarray/substring, longest/shortest	Sliding window
Count subarrays with sum/property	Prefix sum + map
Monotonic condition, "minimum X such that"	Binary search
Next greater/smaller, nesting	(Monotonic) stack
Tree, "for each node"	DFS returning values
Levels, nearest, fewest steps (unweighted)	BFS
Prerequisites, ordering	Topological sort
Components, cycle on add	Union-find
All combinations/arrangements	Backtracking
Top k, k-th, schedule	Heap / greedy
Number of ways, min cost, choices	DP
Weighted shortest path, connect all	Dijkstra / MST

After Week 20

Repeat this week's format indefinitely. Add tries (prefix trees: autocomplete, word search on many words), bit manipulation (XOR tricks, counting bits), and design problems (LRU cache = hash map + doubly linked list) as bonus weeks.