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CPRIME - optimized sieve of eratothenes
TDKPRIME - optimized sieve of eratothenes
PRIMES2 - optimized sieve of eratothenes
FCTRL - number of zeros in factorial n
BRCKTS - BIT, segment tree
BOXES - minimum cost flow, comment: see adrian kuegel's post
STRDIST - DP, optimization
MARBLES - combinatorics, x1 + x2 + ... + xk = n with xi>=1 (1<=i<=k)
DISUBSTR - suffix array, suffix tree
BIA - dominator tree in a flow graph, paper by Lengauer and Tarjan
ASSIST - easy, precalc
REPEATS - KMP, suffix array, comment: for nlogn solution see gawry's post
PT07X - minimum vertex cover of a tree
MINDIST - greedy, graph theory, tree, good
DQUERY - data structues, BIT, segment tree, preprocessing
SEGMENTS - greedy, good
STABARDS - bipartite matching
AE2A - DP, probability, guesswork
GCD - number thoery, interesting
TWOSQRS - number theory, comment: see posts in forums for comparison of different approaches
MAXISET - backtracking, prunning
PALIN - Finding the next palindrome of a given number, SRM 330, Div-2 Hard
POSTERS - line sweep, binary heap, interval tree
MATRIX2 - sliding RMQ, see pegwiki, IOI06 Pyramid
SWAP - BIT, inversions, good
DISPUTES - DP, trick, brute force
INTERVAL - sorting, greedy, binary search
PARITY - bits, math, backtrack
WINDMILL - observation
MAXLN - geometry
BRICKS - merge sort
BYTESE1 - dijkstra
MSTS - bfs, union find, gaussian elimination, chinese remainder theorem, comment: see misofs post
PRMLX - combinatorics, postition of a permutation
ANARC08C - KMP, greedy
VPARTY - maximum matching in general graph, edmond's blossom algorithm, see StevieT's post
MCQUERY - all pairs maximum flow, gomory-hu trees, comment: two other problems using this algorithm can be found at UVa
RACETIME - merget sort, k-th smallest integer, binary search
QMAX3VN - BIT, BST, comment: look at topcoder forum for stjepan's bst solution
GSS6 - similar to QMAX3VN, Treap
CF36D - game of acyclic graph, see codeforces
NOCHANGE - DP, hard, comment: see humblefools explanation / SRM 416, Div 1 500.
STORE - DFS, articulation point
LAZYCOWS - DP, observation, comment: see paladin8's post
MATRIX - optimization, comment: see prunthaban solution, plus seeing this thread wouldn't hurt:
LIM - gaussian Elimination
GS - gaussian Elimination, comment: Look at CEOI 2010 arithmetic rectangles
NWERC04H - gaussian elimination
BANDMATR - gaussian elimination, hell
DOCTOR - gaussian elimination, comment: see NilayVaish, braineter and abstractwiz post, idea is similar to Div-1 Medium SRM 306
CMPLS - lagrange interpolation, gaussian elimination
BMJ - hexagons, patterns
DISTANCE - analysis, brute force, comment: similar to
GSS2 - sotring, segment tree
CTGAME - histogram, stack, binary tree
KQUERY - data structures, sorting the queries
KQUERY2 - data structures, like RACETIME, comment: see decowboy's post on forum for an interesting approach
DQUERY - data structures, sorting the queries
WEIRDFN - heap, priority queue, comment: tc forum says priority queues were slow, but someone solved it with PQ.
ASISTENT - permutation ranking
BABY - min-cost maximum matching, DP, comment: DP is hard to get AC
DIVSUM2 - pollard's rho factorization
QTREE - lca, heavy light decomposition
QTREE3 - segment tree, heavy light decomposition, comment: see stjepan thread, OTOCI is a harder one
OTOCI - heavy light decomposition, harder version of QTREE3
TOUR - transitive closure, comment: transistive closure in O(n^2)
SKYLINE - catalan number
HEAPULM - hard, heap, treap, comment: there is a linear solution, see defrager's comment
LIS2 - coastline algo by misof, comment: read two good post made by venco and bbi5291
NICEDAY - coastline algo by misof, comment: See
FRACTION - farey sequence, comment: see a solution by sql_lall in tc forum based on gcd, closed form is in concrete mathematics
ACS - puzzle
SEQPAR - greedy, good
MRECTCNT - number theory
PAGAIN - number theory, primality testing, miller rabin
PON - number theory, primality testing, miller rabin
PGCD - number theory
LCMSUM - numbet theory, euler totient function
ASSIGN4 - min-cost max-flow
COCONUTS - min-cut
DOMINO2 - inclusion-exclusion, hard
PERMSG - solving system of linear congruence
SUPPER - LIS, good
DPEQN - number theory
INUMBER - number theory, interesting
PRIMIT - graph theory, degree count, comment: read this polish solution :P
LAZYCOWS - dp, good
KGSS - segment tree
KPPOLY - geometry, ternary search
PARTSUM - data structures, good
MINMOVE - lyndon words, comment: see thread posts by blueblimp and others
SUBS - strings, binary search
SCITIES - kuhn-munkres
SUBSUMS - meet in the middle, comment: see LongPipes, the Div 1 hard from SRM 205
LOTTERY - BST, sets, comment: see thread with cpphamza's post
PHONY - number theory, good, comment: see misof's post
HIGH - determinant, kirchoff's matrix tree theorem
MPOLY - DP, geometry
CVXPOLY - DP, geometry
MTRIAREA - DP, geometry
MORSE - DP, trie
CEOI09HA - DP, convex hull optimization, comment: see pegwiki
NKLEAVE - DP, convex hull optimization
SUBST1 - string, lcp, segment tree, suffix array, comment: see manber's article link in tc forum, post by MauricioC and ardiankp
CCOST - BIT, finding a way to change 2D range sum to 1D, comment: see gawry's post in TC
CHASE - geometry, maximum number of points on a line, line-point duality, hashing, comment: see eleusive's post in forums
HORRIBLE - segment tree, lazy propagation
TLE - dp, optimization, comment: if you are stuck, took at StevieT's post
CASHIER - RMQ, deletion
ANARC08I - efficient printing of a walsh matrix
RSORTING - DP, hard, comment: see BOI 2007 booklet, problem: sorting
BOI7SOU - RMQ, nice trick, comment: see BOI 2007 booklet, problem: sound
BOI7FEN - dijkstra, geometry, encircling trick, comment: see BOI 2007 booklet, problem: fence
BOI7ESC - min-cut, maximum flow, dfs, vertex splitting, comment: see BOI 2007 booklet, problem: escape
CONNECTE - matrix exponentiation, comment: link: see BOI 2007 booklet, problem: points
BOI7SEQ - DP, greedy, comment: see BOI 2007 booklet, problem: sequence
EOPERA - IDDFS, comment: similar problem, but ikatanic says this solution is slow
TREESUM - tree, dfs, combinatorics, binomial theorem, comment: see nokia's explanation in forums
SCALES - DP, comment: see StevieT's post
SUMFOUR - given 40000 a's, b's, c's, d's, find how many a+b+c+d=0
TRGRID - pattern, case analysis
WORDEQ - Union-find
MOD - discrete log, baby step giant step
ORDERS - permutation reconstruction, fining k-th remaining item in logN, comment: see gawry's binary tree implementation at forum
ORDERSET - treap, splay tree
OPTM - max flow, comment: Similar to SRM 442 Div 1 Hard
AMATH - number theory, big integer
AMBM - greedy, comment: kinda like FibonacciKnapsack of TC, see moshiur's blog for proof
AMR10E - matrix multiplication, good, comment: amritapuri 2010
ANARC08D - DP, triangular grid
ANARC08J - bruteforce
ANARC08J - sorting
ANARC09F - geometry
ANTTT - graph theory, geometry
AP - bipartite matching, DP, comment: google codejam APAC Semifinal 2008, see ACRush's code
ARCTAN - math
ARITHSEQ - DP, brute force, cycle finding, comment: brute forcable in time limit, observation: cycles
ARRANGE2 - backtrack, heavy optimization, comment: codechef problem
TREECST - graph theory, DP, comment: see COCI 08-09 contest 1, problem KRTICA
BARB - modular arithmetic, brute force
BFALG - modular arithmetic, extended euclid, chinese remainder theorem, fibonacci
BLUEEQ2 - number of solution of an eq k1x1^p1+k2x2^p2+...+knxn^pn where k, p are known
BOBALLS2 - bouncing balls, math
BORW - dp, easy, comment: huge timelimit
BOYSCOUT - DP, geometry
CHOCOLA - greedy, good
KPSUM - DP, digits, comment: pattern solution described by rem in forums(RIP).
DOORSPEN - geometry, convex hull
BSHEE - geometry, convex hull
BULK - geometry, cube, stuff
SEGVIS - geometry, visibility
CONDUIT - geometry, lengths of OR of lines
STONE - geometry, centroid of polygon
RUNAWAY - geometry, largest empty circle
DIRVS - geometry, shortest path
RAIN1 - geometry, envelopes
DRAWQUAD - geometry, max area quadrangle from 10^3 points
TCUTTER - geometry, co-ordinate compression, graph traversal
LITEPIPE - geometry, line segment intersection
RHOMBS - geometry, rhombus, looks hard
FSHEEP - geometry, point in polygon in O(lg n)
FLBRKLIN - geometry, BIT
CERC07P - geometry, sorting, costline?
BAC - geometry, voronoi

Note: I have been following topcoder forum for quite a while. Every time there is an interesting discussion about something (a discussion involving of high rated coders/interesting topics), I created an entry in a text file for future reference. I collected some of the problems from other sources as well. It will help you to set contests. But it is full of spoilers and should not be used extensively for someone’s own training.

-- Mir Wasi Ahmed

PS: I stopped updating this list a while ago.