Graphs -> Euler Tour / Subtree Queries

Flatten one rooted subtree into one contiguous interval so subtree-only queries become array range queries.

• Topic slug: graphs/euler-tour-subtree
• Tutorial page: Open tutorial
• Ladder page: Open ladder
• Repo problems currently tagged here: 1
• Repo companion pages: 4
• Curated external problems: 4

Microtopics

• tin-tout
• single-entry-tour
• subtree-interval
• flatten-tree
• fenwick-on-tour
• subtree-sum
• point-update

Learning Sources

Source	Type
USACO Guide Euler Tour Technique	Reference
OI Wiki tree basics	Reference
CSES Subtree Queries	Practice

Practice Sources

Source	Type
CSES Problem Set	Practice
USACO contest archive	Practice
AtCoder problems archive	Practice

Repo Companion Material

Material	Type
Subtree Queries hot sheet	quick reference
Euler Tour subtree starter route	starter route
Subtree Queries note	anchor note
Trees tutorial	adjacent tutorial

Curated External Problems

Core

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Subtree Queries	CSES	Medium	Trees, Euler Tour	Flatten Tree; Fenwick Tree; Range Sum Queries	Rooted Tree; Fenwick Tree	Subtree Sum; Updates; Fenwick	The canonical subtree-interval problem where flattening a rooted tree turns each subtree into one range query.

Stretch

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Count Descendants	AtCoder	Medium	Trees, Euler Tour	Flatten Tree; Offline Counting; Binary Search	Subtree Intervals; Binary Search	Subtree Interval; Depth Buckets; Offline	A clean next step where subtree intervals stay the same but you intersect them with depth-grouped positions.
Distinct Colors	CSES	Hard	Trees	Flatten Tree; Offline Queries; Subtree Aggregation	Euler Tour; Subtree Intervals; Offline Reasoning	Distinct Values; Subtree Aggregation; Offline	A stretch problem showing that the same subtree interval view can feed a different offline engine once sum/count is no longer enough.

Bridge

Problem	Source	Difficulty	Context	Style	Prerequisites	Tags	Why it fits
Path Queries	CSES	Medium	Trees, Euler Tour	Euler Tour; Fenwick Tree; Prefix On Tree	Tree Flattening; Fenwick Tree; Rooted Tree	Root Path Sum; Updates; Tree Flattening	A strong compare point once subtree intervals are trusted and you want to see how similar flattening ideas answer a different rooted-tree query.

Repo Problems

Code	Title	Fit	Difficulty	Pattern	Note	Solution
SUBTREEQUERIES	Subtree Queries	primary	medium	euler tour flattening; subtree interval; fenwick point set range sum	Note	Code

Regeneration

python3 scripts/generate_problem_catalog.py