Algorithms and computational complexity

Algorithms and the time, memory, queries and other resources needed to solve computational problems.

Individual problems 123

Curated contributions 129

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AI involvement:
AI-centered43AI-led78AI-autonomous8
Importance:
Modest8Notable79Major42
Technical verification:
Reported31Partial16Formal82
Human understanding:
Few70Partial2Full57
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Group constructions cannot refute the Set Cover Conjecture, including tensor powers

For k≥2 and m≥1, a Strassen combinatorial degeneration of a finite group tensor onto the mth tensor power of the balanced tripartitioning tensor T_k requires |G|≥binom(3k,⌊3k/2⌋)^m>τ_k^m, where τ_k=8^k binom(3k,k)binom(2k,k)/27^k. For single-copy group restrictions, |G|≥2^{3k−1}; the partition products factor through commuting elements even when G is nonabelian.

AI involvementAI-led
ImportanceNotable
Technical verificationFormal (Lean)
Human understandingFew

Subexponential Deterministic Factoring

Isaac Rudich, Louis-Martin Rousseau

A single deterministic Turing machine outputs the smallest prime factor Nat.minFac N of every natural number N in binary. For each integer k≥1 there is a constant C_k such that its running time on every n-bit input is at most C_k·2^{⌊n/k⌋}; all stack alphabets are finite. Thus the stated deterministic running time is N^{o(1)}.

AI involvementAI-centered
ImportanceMajor
Technical verificationFormal (Lean 4)
Human understandingFew

Approximate Counting for Mixed p-Spin Glasses in Weak External Fields via Cluster Expansion

Qiang Wu

For SK and finite mixed Ising p-spin models with all interaction orders at least three, at a fixed margin below the second-moment threshold and homogeneous fields |h|≤ρ₀N^{-1/4}, algorithms approximate log Z_N to additive error ε using a number of exact operations polynomial jointly in N, ε^{-1} and δ^{-1}. Symmetric unit-variance disorder is allowed; failure is at most δ plus an explicit disorder-tail term, which vanishes with a finite fourth moment.

AI involvementAI-centered
ImportanceNotable
Technical verificationFormal (human)
Human understandingFull

A 2^{o(n)} Time Algorithm for 3-SAT

Claude

One deterministic finite-alphabet Mathlib TM2 machine exactly counts the satisfying assignments of k-CNF formulas with k≥1, m≥2 distinct clauses and n≥4 occurring variables in time 2^{O(min{k²n log log n/√log n, km/√log m})}, with base-two logarithms and an absolute hidden constant. A separately formalized decision statement refutes ETH.

AI involvementAI-autonomous
ImportanceMajor
Technical verificationFormal (Lean 4)
Human understandingFew

The Euclidean algorithm is not optimal among uniform processes

Jason Davies

For every positive integer pair a≥b, gcd(a,b) has a remainder-only derivation using at most (6+o(1)) log₂(a)/log₂log₂(a) remainder calls, uniformly in b. Previously computed values may be reused and the choice of operands is free. This refutes Moschovakis’s stated uniform-process lower-bound conjectures, not the Main Conjecture for algorithms.

AI involvementAI-autonomous
ImportanceNotable
Technical verificationFormal (Lean)
Human understandingFew

Sum-of-squares minimizers for a left-shift binary GCD algorithm

For each n≥2, among ordered positive integer inputs u≥v>0 taking exactly n iterations of the Shallit–Sorenson left-shift binary GCD algorithm, u²+v² has a unique minimum at (p[n−1],p[n−2]). Here p[0]=1, p[1]=3, and p[j+2]=p[j+1]+p[j] for even j, or 2p[j+1]+p[j] for odd j.

AI involvementAI-led
ImportanceModest
Technical verificationFormal (Lean)
Human understandingFew

Exact Storage-Repair-Bandwidth Tradeoffs for (6,5,5) and (7,6,6) Exact-Repair Regenerating Codes

Chao Tian

The manuscript gives converse bounds that completely characterize the storage/repair-bandwidth tradeoffs of exact-repair regenerating codes for (n,k,d)=(6,5,5) and (7,6,6), without assuming linear codes. Previously known layered codes with space sharing attain the bounds.

AI involvementAI-led
ImportanceNotable
Technical verificationPartial
Human understandingFull

Polynomial Hitting Lists for Noncommutative Rational Formulas

OpenAI

Given unary n and a size bound s, a deterministic machine constructs in polynomial bit time a polynomial-size list of rational matrix tuples of polynomial total output length and common polynomial dimension. Every admissible nonzero noncommutative rational formula over Q of size at most s has a defined, invertible evaluation on a listed tuple.

AI involvementAI-led
ImportanceNotable
Technical verificationFormal (Lean 4 with Mathlib)
Human understandingFew

AI-built Lean program triangulates simple polygons in linear time

For every closed simple polygon with n vertices, including collinear vertices and equal heights, an explicit exact-real-RAM program returns a conforming triangulation with n−2 triangles in at most C(n+1) steps and natural words bounded by K(n+1). It is a variant of Chazelle’s algorithm that completes the visibility map directly below n=2³⁰+2.

AI involvementAI-led
ImportanceNotable
Human understandingFew

AI-assisted proof gives sharp graph-matrix norm orders

For each fixed finite simple graph shape in the globally injective dense independent-sign model and fixed p>0, the pth norm moment has matching upper and lower orders n^((h+i₀−s)/2)log(2n)^(b*/2), with h the role count, i₀ isolated interior roles, s the minimum boundary-separator size and b* the largest attached floating-component count over minimum separators.

AI involvementAI-centered
ImportanceNotable
Human understandingFew

AI-assisted Walsh embedding reaches linear row scaling

For n=2^k, a fixed real orthonormal n×d frame, 0<ε<1 and 0<δ<1/2, two independent sign rerandomizations of the normalized Walsh transform followed by uniform row sampling preserve all squared norms within ε with probability at least 1−δ. The stated row count is min(n,⌈8192(d+27⌈log₄(4d/δ)⌉³)/ε²⌉), which is O(d/ε²) for fixed δ.

AI involvementAI-centered
ImportanceNotable
Human understandingFew

AI-derived bounds for Mazur’s greedy drawing construction

For a well-formed Mazur edge, cycle, series and join scheme with n≥2 vertices and j nontrivial joins, the span satisfies T+1≤2^j(n−2j), with equality at (n,j)=(2,0) or 2j+3≤n. Its worst case is T=2^(n/2)−1 for even n and T=3·2^((n−3)/2)−1 for odd n. Companion theorems give interior dart mass ≤aₛbₛT, Dirichlet row norm ≤2(n−1)²T and |det M|≤(2(n−1)²T)^n, bound the candidate products T²|det M| and T³|det M|, and prove z=adj(M)u with Mz=Δu and boundary zₛ=Δhₛ(T−hₛ) when hₛ≤T, where Δ=det M.

AI involvementAI-led
ImportanceModest
Human understandingFew

AI-developed proof improves the permanent-approximation base

For every nonnegative rational n×n matrix, Anari’s formal development constructs one rational-output algorithm and an absolute constant c<√2 with a two-sided cⁿ approximation guarantee for the permanent. It also proves deterministic polynomial time in the ordinary binary input size.

Formally Verified Autoresearch for Analyzing the Expressivity of Multi-Head Attention

Karthik Viswanathan, Plamen Dimitrov, Stefano Rocca, Sarayu Sirikonda

For the paper’s one-layer, attention-only transformer on Boolean inputs with a dedicated query token and linear threshold readout, the autonomous core results characterize head complexity by sums of admissible linear-fractional functions, bound it below by threshold degree, and determine it exactly for symmetric Boolean functions by the number of sign changes. In particular, n-bit parity requires exactly n heads.

AI involvementAI-autonomous
ImportanceNotable
Technical verificationFormal (Lean)
Human understandingFew

The Exponential Time Hypothesis is False

OpenAI

For each fixed k≥2, one deterministic finite-tape machine exactly counts satisfying assignments of every canonically encoded k-CNF formula on n variables. With encoding length L, its time is (L+1)^{O_k(1)} 2^{O_k(n(log log n)²/√log n)} and its visited tape space is polynomial in L at every execution prefix. In particular, fixed-width 3-SAT has a subexponential-time decision algorithm.

AI involvementAI-led
ImportanceMajor
Technical verificationFormal (Lean)
Human understandingFew

Anthropic reports: Claude reconstructs NIST elliptic-curve seed generation

Anthropic reports recovering a reproducible lrand48-and-timestamp recipe for all five NIST prime-curve seeds, five additional ANSI prime-curve seeds and four NIST binary-curve seeds. The reported timestamps and candidate indices regenerate each 160-bit public seed. The NIST B-163 seed remains unexplained.

AI involvementAI-led
ImportanceNotable
Technical verificationPartial
Human understandingFull

Revisiting Separators in String Graphs, Region Intersection Graphs, and Induced-Minor-Free Graphs

James Davies, Paweł Rzążewski, Jack Spalding-Jamieson, Bartosz Walczak

The AI-origin improvement in Appendix B gives non-expansive line embeddings with O(log h) average distortion for the stated vertex-weighted metrics of connected graphs excluding the one-subdivision of K_h as an induced minor. The paper derives balanced separators of size O(h log h √m) for the corresponding m-edge graphs.

AI involvementAI-centered
ImportanceNotable
Technical verificationFormal (Lean)
Human understandingFull

Explicit circuits for the Walsh–Hadamard transform below the textbook operation count

Jacob Sussman

For every commutative ring R and every k≥0, the exact, unscaled Walsh–Hadamard transform on N=2^k inputs has a straight-line circuit with at most (3/4) N log₂ N + N/4 lines. Each line creates u+c·v or c·v−u from available values, with a fixed ring constant c, and costs one. Reuse, output selection and permutations are free.

AI involvementAI-centered
ImportanceModest
Technical verificationFormal (Lean)
Human understandingFew

Navot: AI-assisted extensions of the 9/4 matrix multiplication bound to fields and rings

Navot’s AI-assisted Lean developments extend OpenAI’s matrix multiplication exponent bound ω ≤ 9/4 from complex numbers to every field, including finite fields and positive characteristic, and subsequently to every associative unital ring, including noncommutative rings. The ring development establishes exact integer coefficient tensor-rank identities and, for every ε > 0, correct division-free arithmetic programs with cost at most C n^(9/4 + ε) at every positive matrix size, for one C independent of n. Palomar registered the field development on 8 October and the ring development on 11 October 2026.

AI involvementAI-centered
ImportanceNotable
Technical verificationFormal (Lean)
Human understandingFew

OpenAI reports a parity-lift reduction for Weisfeiler–Leman equivalence

For each k≥4, an explicit construction maps a finite compatible-choice system to two equal-size simple uncolored graphs that are k-dimensional Weisfeiler–Leman equivalent exactly when the system has no successful choice; a successful choice is detected after two joint-refinement rounds or one separate-refinement round.

AI involvementAI-led
ImportanceNotable
Technical verificationFormal (Lean 4)
Human understandingFew

OpenAI reports a uniform quasipolynomial-time trace-reconstruction decoder

For every binary string of known length n and known rational deletion retention probability p, one randomized algorithm reconstructs the string with probability at least 2/3 using an explicit sample budget and bit time polynomial in that budget and the binary input length; for each fixed p, both are quasipolynomial in n.

AI involvementAI-led
ImportanceNotable
Technical verificationReported
Human understandingFew

OpenAI reports one matrix hitting point in every positive characteristic

Given a prime p in binary and positive n,s in unary, one deterministic polynomial-bit-time machine outputs a tuple of matrices over F_p of dimension O(n³s⁶) that detects every nonzero division-free noncommutative formula of size at most s in n variables over every field of characteristic p.

AI involvementAI-led
ImportanceNotable
Technical verificationReported
Human understandingFew

OpenAI reports a quasilinear PCP theorem for PPAD

There are fixed positive rational ε and δ and a deterministic reduction mapping an End-of-Line instance of binary length N to a generalized circuit of length N(log N)^O(1). A solution to the original instance can be recovered in polynomial time from any polynomial-length rational assignment ε-satisfying all but a δ fraction of gates.

AI involvementAI-led
ImportanceMajor
Technical verificationReported
Human understandingFew

OpenAI reports a memory–sample lower bound for noiseless Gaussian regression

For every fixed A>0 and sufficiently large dimension d, a one-pass learner retaining at most Ad² bits between independent exact Gaussian linear measurements needs at least c_A d log(1/ε) measurements to estimate a uniformly random unit vector to angular error ε≤1/10 with success probability at least 2/3.

AI involvementAI-led
ImportanceNotable
Technical verificationFormal (Lean 4)
Human understandingFew

OpenAI reports QMA-hardness of continuum Coulomb energy

Approximating the electronic Coulomb spectral infimum in three-dimensional continuum space is QMA-hard when positive integer nuclear charges use binary encoding, nuclei have distinct rational positions and electron count is unary; a deterministic polynomial-time reduction produces a promise gap of at least one.

AI involvementAI-led
ImportanceNotable
Technical verificationFormal (Lean 4)
Human understandingFew

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