Wednesday, October 26, 2016

Minesweeper for Linux (just for fun)

Much time has been passed since I last played minesweeper on my Windows machine in the campus... A lot has been changed since that time. Now I use Linux and I'm not in the campus any more :) I just thought: why not to implement this cool game on my own...

Here's what I have now (sources and README):

In this post I would like to share with some interesting moments I faced with during implementation.

Saturday, June 11, 2016

How many numbers in the given interval with a bit set

Problem: given two numbers a and b find how many numbers with a bit x set are there in the interval [a,b].


Input: 5 8 2

Output: 3


5 = 0101
6 = 0110
7 = 0111
8 = 1000

The second bit (starting from the least significant bit with index 0) is set only in numbers 5, 6 and 7, so there are 3 numbers in the interval [5, 8] with the second bit set.


Thursday, March 3, 2016

Remove all merged local branches in Git except master

$ git branch
* master

Here, branch 'c' has not merged with master yet. Let's remove all merged branches:

$ git branch --merged master | grep -v master | xargs git branch -d
Deleted branch a (was ebb9040).
Deleted branch b (was ebb9040).

$ git branch
* master

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
rm -f dmalloc
gcc -o aout dmalloc.o dmalloc_argv.o compat.o env.o \
mv aout dmalloc
rm -f
ld -shared --whole-archive -soname -o 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 '' failed
make: *** [] Error 1

Wednesday, January 13, 2016

dmalloc: compiling and installing a static library


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: Please check-out Makefile and conf.h to make sure that
configure: sane configuration values were a result.
configure: You may want to change values in settings.h before
configure: running 'make'.
configure: To run the basic library tests, you can execute:
configure:   make light
configure: or
configure:   make heavy

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
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.


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


$ 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