thecodingwizard / usaco

Solutions to USACO Training and USACO Contest Problems

USACO Solutions

Solutions to USACO training and USACO contest problems.

USACO Training:

Problem Number	Problem Name	Solution Notes
1.5.1	Arithmetic Progressions	Careful Brute Force
1.6.3	Superprime Rib	Brute force
2.1.1	The Castle	Floodfill to assign each room a number
2.1.2	Ordered Fractions	Generate all possible fractions
2.1.3	Sorting A Three-Valued Sequence	Notes written as comments in code
2.1.4	Healthy Holsteins	Brute force
2.1.5	Hamming Codes	Brute force
2.2.1	Preface Numbering	Brute force
2.2.2	Subset Sums	DP
2.2.3	Runaround Numbers	Brute force
2.2.4	Party Lamps	Brute force 2^4, doesn't matter if you press button twice
2.3.1	Longest Prefix	DP
2.3.2	Cow Pedigrees	DP
2.3.3	Zero Sum	Brute force (DFS)
2.3.4	Money Systems	DP (VN)
2.3.5	Controlling Companies	Recursion
2.4.1	The Tamworth Two	Brute force, maximum (100*4)^2 steps before "impossible"
2.4.2	Overfencing	run shortest path BFS on two exit nodes
2.4.3	Cow Tours	Dijkstra
2.4.4	Bessie Come Home	Dijkstra
2.4.5	Fractions to Decimals	Recursion
3.1.1	Agri-Net	Prim's (or Kruskal)
3.1.2	Score Inflation	Knapsack
3.1.3	Humble Numbers	Create size N set of possible numbers, brute force
3.1.4	Contact	Brute force
3.1.5	Stamps	DP
3.2.1	Factorials	Count number of twos and fives
3.2.2	Stringsobits	Define dp(i, j) = # of numbers with i bits and at most j ones
3.2.3	Spinning Wheels	Brute Force, max 360 seconds
3.2.4	Feed Ratios	Brute force
3.2.5	Magic Squares	BFS
3.2.6	Sweet Butter	APSP
3.3.1	Riding the Fences	Eulerian Path
3.3.2	Shopping Offers	Dijkstra
3.3.3	Camelot	Brute force, king can take only two steps
3.3.4	Home on the Range	DP
3.3.5	A Game	DP
3.4.1	American Heritage	Recursively generate tree
3.4.2	Electric Fence	Pick's Theorem
3.4.3	Raucous Rockers	Brute Force (Bitmasking)
4.1.1	Beef McNuggets	DP
4.1.2	Fence Loops	Dijkstra
4.2.1	Drainage Ditches	Max Flow O(V^2E)
4.2.3	[Job Processing][4.2.3]	Greedy

Silver USACO Contests:

Contest Date	Problem ID	Problem Name	Solution Notes	Score
Feb 2018	reststops	Rest Stops	Greedy	10/10

Gold USACO Contests:

Old USACO Gold (Silver):

Contest Date	Problem ID	Problem Name	Solution Notes	Score
Nov 2012	clumsy	Clumsy Cows	Greedy	16/16
Nov 2012	distant	Distant Pastures	APSP, dijkstra	16/16
Nov 2012	bbreeds	Balanced Cow Breeds	Same problem as Gold	16/16
Dec 2012	crazy	Crazy Fences	Computational Geometry	10/10
Dec 2012	wifi	Wifi Setup	DP	10/10
Dec 2012	mroute	Milk Routing	Dijkstra	10/10
Jan 2013	paint	Painting the Fence	Coordinate Compression, Store Deltas & Sweep	10/10
Jan 2013	squares	Square Overlap	Sweep	10/10
Jan 2013	invite	Party Invitations	precompute which groups each cow is in	10/10
Feb 2013	perimeter	Perimeter	Optimized Floodfill	10/10
Feb 2013	tractor	Tractor	Binary search for answer, dfs	10/10
Feb 2013	msched	Milk Scheduling	Greedy	10/10
Mar 2013	poker	Poker Hands	Greedy	10/10
Mar 2013	painting	Farm Painting	Sweep	10/10
Mar 2013	cowrun	The Cow Run	DP, same as gold	15/15
Open 2013	gravity	What's Up With Gravity?	Dijkstra	10/10
Open 2013	fuel	Fuel Economy	Greedy	10/10
Open 2013	cruise	Luxury River Cruise	Find where sequence repeats	10/10
Nov 2013	nocow	Farmer John has no Large Brown Cow	Solvable with a bit of math	10/10
Nov 2013	crowded	Crowded Cows	Sweep, can use multiset instead of monotonic queue	11/11
Nov 2013	pogocow	Pogo-Cow	DP, note that Bessie can go either direction	11/11
Dec 2013	msched	Milk Scheduling	Greedy, sweep	11/11
Dec 2013	vacation	Vacation Planning	Code is slightly modified from gold version, answer is unnecessarily complicated for silver	10/10
Dec 2013	shuffle	The Bessie Shuffle	Repeated Squaring, Permutations, Composing functions/permutations	10/10
Jan 2014	slowdown	Bessie Slows Down	Maintain two arrays, simulation	10/10
Jan 2014	ccski	Cross Country Skiing	Prim's	10/10
Jan 2014	recording	Recording the Moolympics	Greedy	10/10
Feb 2014	auto	Auto-complete	Binary search	10/10
Feb 2014	rblock	Roadblock	Dijkstra	10/10
Feb 2014	scode	Secret Code	DP	10/10
Mar 2014	irrigation	Watering the Fields	Kruskal/MST	10/10
Mar 2014	lazy	The Lazy Cow	Rotate grid 45 degrees	10/10
Mar 2014	mooomoo	Mooo Moo	DP	10/10
Open 2014	fairphoto	Fair Photography	Sweep	10/10
Open 2014	gpsduel	Dueling GPSs	Dijkstra	10/10
Dec 2014	piggyback	Piggy Back	Shortest Path on three nodes	11/11
Dec 2014	cowjog	Cow Jog	Sweep	15/15
Jan 2015	stampede	Stampede	Sweep	15/15
Jan 2015	cowroute	Cow Routing	Dijkstra	12/12
Jan 2015	meeting	Meeting Time	DP	15/15
Feb 2015	censor	Censoring	Rolling Hash	15/15
Feb 2015	hopscotch	Cow Hopscotch	DP	15/15
Feb 2015	superbull	Superbull	MST, Prim's O(V^2)	10/10
Open 2015	bgm	Bessie Goes Moo	Parity	10/10
Open 2015	trapped	Trapped in the Haybales (Silver)	Sort, Sweep	14/14

USACO Gold (2015-now)

Contest Date	Problem ID	Problem Name	Solution Notes	Score
Dec 2015	cardgame	High Card Low Card (Gold)	Greedy	15/15
Dec 2015	feast	Fruit Feast	DP (Knapsack)	12/12
Dec 2015	dream	Bessie's Dream	Dijkstra	16/16
Jan 2016	radio	Radio Contact	DP	10/10
Feb 2016	cbarn	Circular Barn	Greedy	10/10
Feb 2016	cbarn2	Circular Barn (Revisited)	DP	10/10
Feb 2016	fencedin	Fenced In	MST (Kruskal)	10/10
Open 2016	split	Splitting The Field	Sweep	10/10
Open 2016	closing	Closing The Farm	UFDS (Note: Runs really close to time limit)	10/10
Open 2016	248	248	DP	12/12
Dec 2016	moocast	Moocast	UFDS, brute force	10/10
Dec 2016	checklist	Cow Checklist	DP	10/10
Dec 2016	lasers	Lasers and Mirrors	BFS	11/11
Jan 2017	bphoto	Balanced Photo	Fenwick Tree	10/10
Jan 2017	hps	Hoof, Paper, Scissors	3D DP	10/10
Jan 2017	cownav	Cow Navigation	BFS	10/10
Feb 2017	visitfj	Why Did The Cow Cross The Road	Dijkstra	11/11
Feb 2017	nocross	Why Did The Cow Cross The Road II	DP	10/10
Feb 2017	circlecross	Why Did The Cow Cross The Road III	Fenwick Tree (BIT)	10/10
Open 2017	cownomics	Bovine Genomics	Rolling Hash	10/10
Open 2017	art2	Modern Art 2	Calculate start/end points	10/10
Dec 2017	piepie	A Pie For A Pie	BFS, binary search	10/10
Dec 2017	barnpainting	Barn Painting	DP	10/10
Dec 2017	hayfeast	Haybale Feast	Two Pointers	10/10
Jan 2018	mootube	MooTube	UFDS	10/10
Jan 2018	atlarge	Cow At Large	DFS/BFS	13/13
Jan 2018	spainting	Stamp Painting	DP, recurrence	12/12
Feb 2018	snowboots	Snow Boots	Sort, Doubly-Linked List	12/12
Feb 2018	dirtraverse	Directory Traversal	DFS	10/10
Feb 2018	taming	Taming The Herd	DP	11/11
Open 2018	sort	Out of Sorts	BIT	10/10
Open 2018	milkorder	Milking Order	Topological Sort (Lexicographically earliest)	10/10
Open 2018	talent	Talent Show	Binary search for answer, DP	10/10

Platinum USACO Contests:

Old USACO Platinum (Gold):

Contest Date	Problem ID	Problem Name	Solution Notes	Score
Nov 2012	bbreeds	Balanced Cow Breeds	DP	16/16
Dec 2012	gangs	Gangs of Istanbull/Cowstantinople	Greedy	12/12
Dec 2012	first	First!	trie, checking DAG for cycles	12/12
Dec 2012	runaway	Running Away From the Barn		10/10
Jan 2013	lineup	Cow Lineup	sweep with two pointers	10/10
Jan 2013	island	Island Travels	bfs	11/11
Jan 2013	seating	Seating	Binary Tree, Lazy Propagation	10/10
Feb 2013	partition	Partitioning The Farm	DP	17/17
Feb 2013	taxi	Taxi	Min Cost Matching, calculate distance driven w/o cow	12/12
Feb 2013	route	Route Designing	DP	10/10
Mar 2013	cowrun	The Cow Run	DP	14/14
Mar 2013	hillwalk	Hill Walk	Line sweep, find a way to order hills	12/12
Nov 2013	nochange	No Change	DP, 2^k state	13/13
Nov 2013	sight	Line of Sight	If two cows can see the same point on the silo, they can see each other	11/11
Nov 2013	empty	Empty Stalls	Sweep	11/11
Dec 2013	vacationgold	Vacation Planning (Gold)	Dijkstra	10/10
Dec 2013	optmilk	Optimal Milking	Binary Tree	11/11
Jan 2014	skicourse	Building A Ski Course	DP	10/10
Jan 2014	skilevel	Ski Course Rating	Kruskal	10/10
Feb 2014	rblock	Roadblock	Dijkstra	10/10
Feb 2014	dec	Cow Decathlon	DP	10/10
Mar 2014	sabotage	Sabotage	Binary search, 1D max sum	14/14
Mar 2014	fcount	Counting Friends	Brute Force, greedily connect friends	11/11
Dec 2014	guard	Guard Mark	DP	12/12
Dec 2014	marathon	Marathon	Segment Tree	10/10
Dec 2014	cowjog	Cow Jog	Longest Non-Increasing Subsequence	14/14
Jan 2015	cowrect	Cow Rectangles	Sweep, assume we have to take one of the Holsteins	14/14
Jan 2015	movie	Moovie Mooving	DP, bitmasking	14/14
Open 2015	palpath	Palindromic Paths	DP	12/12
Open 2015	trapped	Trapped in the Haybales	Sort haybales by weight	15/15
Open 2015	buffet	Bessie's Birthday Buffet	DP	15/15

USACO Platinum (2015-now):

Contest Date	Problem ID	Problem Name	Solution Notes	Score
Dec 2015	maxflow	Max Flow	LCA, prefix sums	15/15
Dec 2015	cardgame	High Card Low Card	Greedy	15/15
Dec 2015	haybales	Counting Haybales	Seg Tree, Lazy, Min Query & Sum Query	10/10
Jan 2016	fortmoo	Fort Moo	DP/Sliding Window	13/13
Jan 2016	mowing	Mowing The Field	2D Range Tree	10/10
Feb 2016	balancing	Load Balancing	Binary Search, BIT	15/15
Feb 2016	fencedinplat	Fenced In		10/10
Open 2016	262144	262144	DP	12/12
Dec 2016	team	Team Building	DP	9/9
Jan 2017	promote	Promotion Counting	BIT on preorder of tree	10/10
Jan 2017	tallbarn	Building a Tall Barn	Binary Search	12/12
Jan 2017	subrev	Subsequence Reversal	DP	10/10
Feb 2017	mincross	Why Did The Cow Cross The Road	Fenwick Tree	10/10
Feb 2017	nocross	Why Did The Cow Cross The Road II	DP, RMQ (Seg Tree)	10/10

Note: Code primarily written in C++.