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Documents authored by Itoh, Toshiya

Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2025.94
A Nearly Optimal Deterministic Algorithm for Online Transportation Problem

Authors: Tsubasa Harada and Toshiya Itoh

Published in: LIPIcs, Volume 334, 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)

Abstract
For the online transportation problem with m server sites, it has long been known that the competitive ratio of any deterministic algorithm is at least 2m-1. Kalyanasundaram and Pruhs conjectured in 1998 that a deterministic (2m-1)-competitive algorithm exists for this problem, a conjecture that has remained open for over two decades. In this paper, we propose a new deterministic algorithm for the online transportation problem and show that it achieves a competitive ratio of at most 8m-5. This is the first O(m)-competitive deterministic algorithm, coming close to the lower bound of 2m-1 within a constant factor.
Cite as

Tsubasa Harada and Toshiya Itoh. A Nearly Optimal Deterministic Algorithm for Online Transportation Problem. In 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 334, pp. 94:1-94:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{harada_et_al:LIPIcs.ICALP.2025.94,
  author =	{Harada, Tsubasa and Itoh, Toshiya},
  title =	{{A Nearly Optimal Deterministic Algorithm for Online Transportation Problem}},
  booktitle =	{52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)},
  pages =	{94:1--94:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-372-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{334},
  editor =	{Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.94},
  URN =		{urn:nbn:de:0030-drops-234712},
  doi =		{10.4230/LIPIcs.ICALP.2025.94},
  annote =	{Keywords: Online algorithms, Competitive analysis, Online metric matching, Online weighted matching, Online minimum weight perfect matching, Online transportation problem, Online facility assignment, Greedy algorithm}
}
Document
DOI: 10.4230/LIPIcs.FUN.2022.24
How to Physically Verify a Rectangle in a Grid: A Physical ZKP for Shikaku

Authors: Suthee Ruangwises and Toshiya Itoh

Published in: LIPIcs, Volume 226, 11th International Conference on Fun with Algorithms (FUN 2022)

Abstract
Shikaku is a pencil puzzle consisting of a rectangular grid, with some cells containing a number. The player has to partition the grid into rectangles such that each rectangle contains exactly one number equal to the area of that rectangle. In this paper, we propose two physical zero-knowledge proof protocols for Shikaku using a deck of playing cards, which allow a prover to physically show that he/she knows a solution of the puzzle without revealing it. Most importantly, in our second protocol we develop a general technique to physically verify a rectangle-shaped area with a certain size in a rectangular grid, which can be used to verify other problems with similar constraints.
Cite as

Suthee Ruangwises and Toshiya Itoh. How to Physically Verify a Rectangle in a Grid: A Physical ZKP for Shikaku. In 11th International Conference on Fun with Algorithms (FUN 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 226, pp. 24:1-24:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{ruangwises_et_al:LIPIcs.FUN.2022.24,
  author =	{Ruangwises, Suthee and Itoh, Toshiya},
  title =	{{How to Physically Verify a Rectangle in a Grid: A Physical ZKP for Shikaku}},
  booktitle =	{11th International Conference on Fun with Algorithms (FUN 2022)},
  pages =	{24:1--24:12},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-232-7},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{226},
  editor =	{Fraigniaud, Pierre and Uno, Yushi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2022.24},
  URN =		{urn:nbn:de:0030-drops-159947},
  doi =		{10.4230/LIPIcs.FUN.2022.24},
  annote =	{Keywords: Zero-knowledge proof, Card-based cryptography, Shikaku, Puzzles, Games}
}
Document
DOI: 10.4230/LIPIcs.FUN.2021.22
Physical Zero-Knowledge Proof for Numberlink

Authors: Suthee Ruangwises and Toshiya Itoh

Published in: LIPIcs, Volume 157, 10th International Conference on Fun with Algorithms (FUN 2021) (2020)

Abstract
Numberlink is a logic puzzle for which the player has to connect all pairs of cells with the same numbers by non-crossing paths in a rectangular grid. In this paper, we propose a physical protocol of zero-knowledge proof for Numberlink using a deck of cards, which allows a player to physically show that he/she knows a solution without revealing it. In particular, we develop a physical protocol to count the number of elements in a list that are equal to a given secret value without revealing that value, the positions of elements in the list that are equal to it, or the value of any other element in the list. Our protocol can also be applied to verify the existence of vertex-disjoint paths connecting all given pairs of endpoints in any undirected graph.
Cite as

Suthee Ruangwises and Toshiya Itoh. Physical Zero-Knowledge Proof for Numberlink. In 10th International Conference on Fun with Algorithms (FUN 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 157, pp. 22:1-22:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

Copy BibTex To Clipboard

@InProceedings{ruangwises_et_al:LIPIcs.FUN.2021.22,
  author =	{Ruangwises, Suthee and Itoh, Toshiya},
  title =	{{Physical Zero-Knowledge Proof for Numberlink}},
  booktitle =	{10th International Conference on Fun with Algorithms (FUN 2021)},
  pages =	{22:1--22:11},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-145-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{157},
  editor =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2021.22},
  URN =		{urn:nbn:de:0030-drops-127836},
  doi =		{10.4230/LIPIcs.FUN.2021.22},
  annote =	{Keywords: Zero-knowledge proof, Card-based cryptography, Numberlink, Puzzles, Games}
}
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