Foundations -> Two Pointers¶

Exploit monotone movement to replace nested loops with linear scans, sliding windows, or opposite-end sweeps.

Microtopics¶

Source	Type
USACO Guide two pointers	`Reference`
Competitive Programmer's Handbook	`Reference`

Source	Type
Codeforces two-pointers tag	`Practice`
CSES Problem Set	`Practice`

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Playlist	`CSES`	`Medium`	Sliding Window	Implementation-Heavy; Proof-Heavy	Two Pointers; Hash Maps; Window Invariants	Distinctness; Subarrays; Distinct	A clean sliding-window benchmark where the main skill is maintaining the window invariant.
Subarray Sums I	`CSES`	`Medium`	Sliding Window	Implementation-Heavy	Two Pointers; Positive Numbers; Window Sums	Subarrays; Positive-Sums; Positive-Array	A standard positive-array window problem that helps lock in the expand-shrink pattern.
Sum of Two Values	`CSES`	`Medium`	-	Implementation-Heavy	Sorting; Hash Maps; Pair Sums	Pair-Sum; Hash-Map	A common first pair-sum problem that can be solved with either hashing or sorted two pointers.

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Sliding Window Distinct Values	`CSES`	`Medium`	-	Implementation-Heavy	Two Pointers; Frequency Maps; Window Maintenance	Sliding-Window; Frequency-Counting; Distinct-Count	A direct sliding-window variant that reinforces the same pattern with a slightly different output.

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Ferris Wheel	`CSES`	`Easy`	-	Greedy-Heavy	Sorting; Two Pointers; Greedy Matching	Pairing	A textbook two-pointer pairing problem that is easy to teach and easy to reuse.
Distinct Values Subarrays	`CSES`	`Medium`	Sliding Window	Proof-Heavy; Implementation-Heavy	Two Pointers; Frequency Counts; Subarray Counting	Distinctness; Distinct-Count	A classic counting-by-window problem that builds strong two-pointer intuition.

Code	Title	Fit	Difficulty	Pattern	Note	Solution
`APARTMENTS`	Apartments	`primary`	`easy-medium`	two sorted pointers; tolerance matching; greedy monotone scan	Note	Code
`FERRISWHEEL`	Ferris Wheel	`secondary`	`easy-medium`	opposite end pointers; greedy pairing; sorted capacity matching	Note	Code
`SUMOFTWOVALUES`	Sum of Two Values	`primary`	`medium`	sort and scan; opposite end pointers; index restoration	Note	Code
`TFIELD`	Ruộng bậc thang	`secondary`	`hard`	nested polygons; weighted sliding window; shoelace preprocessing	Note	Code

python3 scripts/generate_problem_catalog.py