arXivDaily arXiv每日学术速递 周一至周五更新
arXiv周末暂无论文更新,休息一下吧,周末愉快~~
arXiv 0810.0906cs.DS
收藏

树的L(2,1)-标号的线性时间算法

A linear time algorithm for L(2,1)-labeling of trees

Toru Hasunuma, Toshimasa Ishii, Hirotaka Ono, Yushi Uno

摘要:

图$G$的L(2,1)-标号是从顶点集$V(G)$到非负整数集的一个赋值$f$,使得对于$V(G)$中的所有$x$和$y$,如果$x$和$y$相邻,则为$|f(x)-f(y)|\ge 2$,如果$x$和$y$的距离为2,则为$|f(x)-f(y)|\ge 1$.一个$k$ -L(2,1)-标号是一个赋值$f:V(G)\to\{0,..., k\}$,L(2,1)-标号问题要求在所有可能的赋值中最小的$k$,我们用$λ(G)$表示.众所周知,这个问题是NP-困难的,即使图的树宽为2,树是一个非常少的类,其中的问题是多项式可解的。最著名的树算法的运行时间是$\mO(Δ^{4.5} n)$,然而,$\mO(n^{1.75})$ -时间算法已经提出了十多年,它大大改善了以前的一个,其中$Δ$是$T$和$n=|V(T)|$的最大程度。本文最后建立了树的L(2,1)-标号的线性时间算法。

英文摘要:

An L(2,1)-labeling of a graph $G$ is an assignment $f$ from the vertex set $V(G)$ to the set of nonnegative integers such that $|f(x)-f(y)|\ge 2$ if $x$ and $y$ are adjacent and $|f(x)-f(y)|\ge 1$ if $x$ and $y$ are at distance 2, for all $x$ and $y$ in $V(G)$. A $k$-L(2,1)-labeling is an assignment $f:V(G)\to\{0,..., k\}$, and the L(2,1)-labeling problem asks the minimum $k$, which we denote by $λ(G)$, among all possible assignments. It is known that this problem is NP-hard even for graphs of treewidth 2, and tree is one of a very few classes for which the problem is polynomially solvable. The running time of the best known algorithm for trees had been $\mO(Δ^{4.5} n)$ for more than a decade, however, an $\mO(n^{1.75})$-time algorithm has been proposed recently, which substantially improved the previous one, where $Δ$ is the maximum degree of $T$ and $n=|V(T)|$. In this paper, we finally establish a linear time algorithm for L(2,1)-labeling of trees.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑