Fix small mistakes discovered in Unit 24

be-oi · Apr 16, 2016 · fcab0f8 · fcab0f8
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diff --git a/24-number-theory/README.md b/24-number-theory/README.md
@@ -13,7 +13,7 @@ This unit covers aspects of number theory that are useful in programming contest
 ## Practice problems
 
 ### Easy
-- UVa 544 - [Goldbach's Conjecture](https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=484) (sieve)
+- UVa 543 - [Goldbach's Conjecture](https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=484) (sieve)
 - UVa 583 - [Prime factors](https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=524) (sieve + factorization)
 - UVa 11827 - [Maximum GCD](https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=2927)
 - UVa 10104 - [Euclid Problem](https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=1045) (extended Euclid)

diff --git a/24-number-theory/number-theory.pdf b/24-number-theory/number-theory.pdf
diff --git a/24-number-theory/number-theory.tex b/24-number-theory/number-theory.tex
@@ -169,13 +169,13 @@ \section{Sieve of Eratosthenes}
 \item Complexity is $O(\sqrt{n}\,/\log n)$ because the density of primes is proportional to $1\,/ \log n$
 \end{itemize}
 \begin{lstlisting}
-// Only called for n < MAXN*MAXN
+// Only called for n < (last prime)^2
 bool isPrime(int n)
 {
     if (n < MAXN)
         return bs[n];
-    for (int i : primes)
-        if (n % i == 0)
+    for (int i=0; primes[i]*primes[i] <= n; i++)
+        if (n % primes[i] == 0)
             return false;
     return true;
 }
@@ -333,7 +333,7 @@ \section{Extended Euclid}
 \item First solution: $x=1, y=-1$
 \item Formula: $(x+2n,\ y-3n)$
 \item Positive $n$: $(3,-4), (5,-7), (7,-10) \ldots$
-\item Negative $n$: $(-1, 2), (-3, 5), (-5, 8) \ldots$
+\item Negative $n$: $(-1, 3), (-3, 5), (-5, 8) \ldots$
 \end{itemize}
 \end{frame}