SPOJ List
Updated automatically every 5 minutes

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
ONEZERO - BFS
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
NHAY - KMP
PERIOD - KMP
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
MINUS - DP
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
MST - MST
BLINNET - MST
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: http://acm.uva.es/board/viewtopic.php?t=5811
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
LUCKYNUM - BFS
SSHUFFLE - DP
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
QTREE2 -
QTREE3 - segment tree, heavy light decomposition, comment: see stjepan thread, OTOCI is a harder one
QTREE4 -
OTOCI - heavy light decomposition, harder version of QTREE3
TOUR - transitive closure, comment: transistive closure in O(n^2)
SKYLINE - catalan number
MINCOUNT - math
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 http://www.algorithmist.com/index.php/LA_3525
FRACTION - farey sequence, comment: see a solution by sql_lall in tc forum based on gcd, closed form is in concrete mathematics
ACS - puzzle
SQRBR - DP
TWENDS - DP
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
COURIER - DP
DOMINO2 - inclusion-exclusion, hard
PERMSG - solving system of linear congruence
SUPPER - LIS, good
DPEQN - number theory
INUMBER - number theory, interesting
LAZYCOWS - dp, good
INTERVALS - sets
KGSS - segment tree
KPPOLY - geometry, ternary search
PALSEC - DP
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
SAMER08D - DP
HIGH - determinant, kirchoff's matrix tree theorem
MPOLY - DP, geometry
CVXPOLY - DP, geometry
MTRIAREA - DP, geometry
MORSE - DP, trie
RENT - DP, BIT
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: http://vn.spoj.pl/problems/CONNECTE/ see BOI 2007 booklet, problem: points
BOI7SEQ - DP, greedy, comment: see BOI 2007 booklet, problem: sequence
EOPERA - IDDFS, comment: similar problem www.hsin.hr/2010/coci/contest2_tasks.pdf, 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
BITMAP - BFS
WORDEQ - Union-find
M00PAIR - DP
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
ALL - BFS
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
BOOKCASE - DP, good
BORW - dp, easy, comment: huge timelimit
BOYSCOUT - DP, geometry
BRCKGAME - DP, good
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