Sunday, January 31, 2016

A fast way to find out whether two elements in matrix share the same diagonal

Let's have the following matrix:

     1 2 3 4 5
     -----------
1 | 0 0 0 0 0
2 | 0 0 1 0 0
3 | 0 0 0 0 0
4 | 1 0 0 0 0
5 | 0 0 0 0 0

with two points: (x1, y1) = (2, 3) and (x2, y2) = (4, 1).

The fastest way to find out whether these two points share the same diagonal is the result of this expression:

bool result = (x1 + y1 == x2 + y2) or (x1 - y1 == x2 - y2)

Now let's complicate the task. Given matrix n x n with m points, find the minimum number of diagonals which contain at least two points. The first line of the input contains: n m. The next m lines contain points with coordinates (xi, yi).

Saturday, January 16, 2016

dmalloc: compiling and installing a dynamic (shared) library

See the previous post: dmalloc: compiling and installing a static library

"dmalloc.h:484:7: error: expected identifier or..." problem is already solved in that post.

Now let's compile and install a shared library

dmalloc-5.5.2]$ ./configure --enable-shlib

dmalloc-5.5.2]$ make shlib
...
gcc -g -O2 -DHAVE_STDARG_H=1 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1 -DHAVE_UNISTD_H=1 -DHAVE_SYS_MMAN_H=1 -DHAVE_SYS_TYPES_H=1 -DHAVE_W32API_WINBASE_H=0 -DHAVE_W32API_WINDEF_H=0 -DHAVE_SYS_CYGWIN_H=0 -DHAVE_SIGNAL_H=1 -I. -I. -c dmalloc_argv.c -o ./dmalloc_argv.o
rm -f dmalloc
gcc -o aout dmalloc.o dmalloc_argv.o compat.o env.o \
-L.
mv aout dmalloc
rm -f libdmalloc.so libdmalloc.so.t
ld -shared --whole-archive -soname libdmalloc.so -o libdmalloc.so.t libdmalloc.a arg_check.o compat.o dmalloc_rand.o dmalloc_tab.o env.o heap.o chunk.o error.o malloc.o
ld: libdmalloc.a(arg_check.o): relocation R_X86_64_32 against `.rodata.str1.8' can not be used when making a shared object; recompile with -fPIC
libdmalloc.a(arg_check.o): error adding symbols: Bad value
Makefile:259: recipe for target 'libdmalloc.so' failed
make: *** [libdmalloc.so] Error 1


Wednesday, January 13, 2016

dmalloc: compiling and installing a static library

dmallochttp://dmalloc.com/

Installation (on Fedora 21 x86_64)

$ uname -irs

Linux 3.18.3-201.fc21.x86_64 x86_64

$ tar -zxvf dmalloc-5.5.2.tgz
dmalloc-5.5.2]$ cd dmalloc-5.5.2/
dmalloc-5.5.2]$ ./configure
configure: configurations for the dmalloc library
configure: build utilities
checking for gcc... gcc
...
checking for strtok... yes
configure: creating ./config.status
config.status: creating Makefile
config.status: creating conf.h
config.status: executing dmalloc.h.2 commands
config.status: executing settings.h commands
configure: 
configure: Please check-out Makefile and conf.h to make sure that
configure: sane configuration values were a result.
configure: 
configure: You may want to change values in settings.h before
configure: running 'make'.
configure: 
configure: To run the basic library tests, you can execute:
configure:   make light
configure: or
configure:   make heavy
configure:

dmalloc-5.5.2]$ make
rm -f dmalloc.h dmalloc.h.t
cat ./dmalloc.h.1 dmalloc.h.2 ./dmalloc.h.3 > dmalloc.h.t
mv dmalloc.h.t dmalloc.h
rm -f arg_check.o
gcc -g -O2  -DHAVE_STDARG_H=1 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1 -DHAVE_UNISTD_H=1 -DHAVE_SYS_MMAN_H=1 -DHAVE_SYS_TYPES_H=1 -DHAVE_W32API_WINBASE_H=0 -DHAVE_W32API_WINDEF_H=0 -DHAVE_SYS_CYGWIN_H=0 -DHAVE_SIGNAL_H=1  -I. -I.  -c arg_check.c -o ./arg_check.o
In file included from /usr/include/string.h:634:0,
                 from arg_check.c:33:
dmalloc.h:484:7: error: expected identifier or ‘(’ before ‘__extension__’
 char *strndup(const char *string, const DMALLOC_SIZE len);
       ^
Makefile:362: recipe for target 'arg_check.o' failed
make: *** [arg_check.o] Error 1

Thursday, May 14, 2015

Convert images to pdf and back

Today I found out a simple and flexible tool which converts images to pdf and vice versa - convert. It was already built in my Fedora 21.

Example:

Let's say I have 1.jpg, 2.jpg, 3.jpg files. To convert them into a single result.pdf run the following command:

$ convert 1.jpg 2.jpg 3.jpg result.pdf

or

$ convert {1..3}.jpg result.pdf

Now I want to get my images back from the result.pdf:

$ convert -density 300 result.pdf image.jpg

where "-density 300" is a precision in points per inch. Each pdf page will be converted into a separate image.

convert supports a lot of different flags and options. To learn more about it:

$ man convert

or

Wednesday, April 1, 2015

log4j2: line separator in header's parameter of PatternLayout

Log4j2 provides a new parameter for PatternLayout:

Parameter name: header
Type: String
Description: the optional header string to include at the top of each log file

With the following log4j2.xml configuration:

1
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<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="20">
    <Appenders>
        <RollingRandomAccessFile name="file" fileName="logs/app.log" filePattern="logs/app-%d_%i.log.gz">
            <PatternLayout>
                <header>
Version: ${env:APP_RELEASE_VERSION}
                </header>
                <pattern>%message%n</pattern>
            </PatternLayout>
            <Policies>
                <OnStartupTriggeringPolicy/>
            </Policies>
        </RollingRandomAccessFile>
    </Appenders>
    <Loggers>
        <Root level="debug">
            <AppenderRef ref="file"/>
        </Root>
    </Loggers>
</Configuration>

Git: undo the last rebase

$ git reflog

f0d821f HEAD@{0}: commit_a
2ea24f8 HEAD@{1}: commit_b
0c3cd49 HEAD@{2}: commit_c
de5b02a HEAD@{3}: commit_d

Suppose that "commit_c" was the head commit of the branch just before the rebase. Let's reset the current branch to this commit:

$ git reset --hard HEAD@{2}

Playing with vim configuration for C++

What I got as a result:


The main features:
  • embedded file system explorer
  • syntax highlighting
  • hotkeys for compiling/running C++ code