diff --git a/src/Advanced/De Bruijn/parts/0 intro.tex b/src/Advanced/De Bruijn/parts/0 intro.tex index 10ed2c7..d669ce7 100644 --- a/src/Advanced/De Bruijn/parts/0 intro.tex +++ b/src/Advanced/De Bruijn/parts/0 intro.tex @@ -21,7 +21,7 @@ Unlock this lock with only 5 keypresses. \end{solution} \vfill -Now, consider the same lock, now set with a three-digit binary code. +Now consider the same lock, but configured with a three-digit binary code. \problem{} How many codes are possible? \vfill diff --git a/src/Advanced/De Bruijn/parts/1 words.tex b/src/Advanced/De Bruijn/parts/1 words.tex index 527cd10..8e56ec1 100644 --- a/src/Advanced/De Bruijn/parts/1 words.tex +++ b/src/Advanced/De Bruijn/parts/1 words.tex @@ -20,7 +20,11 @@ We say $v$ is a \textit{subword} of $w$ if $v$ is contained in $w$. \par For example, \texttt{11} is a subword of \texttt{011}, but \texttt{00} is not. \definition{} -Recall \ref{lockproblem}. Let's generalize this to the \textit{$n$-subword problem}: \par +Recall the lock problem from the previous page. +Let's generalize this to the \textit{$n$-subword problem}: + +\vspace{1mm} + Given an alphabet $A$ and a positive integer $n$, we want a word over $A$ that contains all possible length-$n$ subwords. The shortest word that solves a given $n$-subword problem is called the \textit{optimal solution}. @@ -67,7 +71,7 @@ Find the following: \problem{} Let $w$ be a word over an alphabet of size $k$. \par -Prove the following: +Show that all of the following are true: \begin{itemize} \item $\mathcal{S}_n(w) \leq k^n$ \item $\mathcal{S}_n(w) \geq \mathcal{S}_{n-1}(w) - 1$ @@ -103,7 +107,7 @@ Prove the following: \definition{} Let $v$ and $w$ be words over the same alphabet. \par -The word $vw$ is the word formed by writing $v$ after $w$. \par +The word $vw$ is the word formed by writing $w$ after $v$. \par For example, if $v = \texttt{1001}$ and $w = \texttt{10}$, $vw$ is $\texttt{100110}$. \problem{} @@ -116,7 +120,6 @@ We'll call this the \textit{Fibonacci word} of order $k$. \item What are $F_3$, $F_4$, and $F_5$? \item Compute $\mathcal{S}_0$ through $\mathcal{S}_5$ for $F_5$. \item Show that the length of $F_k$ is the $(k + 2)^\text{th}$ Fibonacci number. \par - \hint{Induction.} \end{itemize} \begin{solution}