StoneWall is an interesting problem that requires some brain cycles yet not too complex. It is good software engineer interview question. Here is a C++ solution whose complexity is O(N). #include <stack> int solution(std::vector<int> &H) { int stones = 0; std::stack<int> heights; for (auto h: H) { while (!heights.empty() && h < heights.top()) { heights.pop();…
Static linking is preferred for some cases although it has its own various problems. Static building/linking is not always possible for some languages on some platform. For OCaml, the answer to this question is yes. In this post, we will introduce 2 methods to statically linking OCaml: static linking with runtime glibc required and static…
Vim opens file even if the user does bot have write permission to the file. But after revision, how to write file content with sudo in Vim if Vim reports no permission to write the file. Use this command inside of vim to write to the file with sudo: :w !sudo tee % Here, !…
Zlib is a popular open-source compression library used by many software applications to compress and decompress data. While it can be installed in Ubuntu using the apt package manager, you may need to install it from the source code if the version available in the Ubuntu repositories is outdated or if you need to customize…
Sparse files are common in Linux/Unix and are also supported by Windows (e.g. NTFS) and macOSes (e.g. HFS+). Sparse files uses storage efficiently when the files have a lot of holes (contiguous ranges of bytes having the value of zero) by storing only metadata for the holes instead of using real disk blocks. They are…
Any good debugger for Python that is like gdb so that the code can be executed step by step for debugging purpose? You might check pdb. You can debug a program such as prog.py by invoking it through pdb: python -m pdb prog.py Common gdb commands can be found in pdb: (Pdb) h Documented commands…
How to test a path (a file or directory exists) in C++? In Bash, the [ -f ] and [ -d ] tests can test whether a file or a directory exist. What are the corresponding C++ ways for these tests? To test whether a file or dir (a path) exists, you may call stat()…
How to create a file if not exist and open it in read and write modes in C++? For example, I would like open a fstream on /tmp/cache to be able to read it and append to it. If the file does not exist yet, create one. A simple code like std::fstream fs(“/tmp/cache”, std::ios::in |…
C++11 requires that lambda function parameters be declared with concrete types. This is sometimes annoying. auto is really nice, especially when the type is complex like std::vector<std::string>::iterator is quite long to type. I know C++14 allows auto in lambda functions. But how to not use concrete types in lambda function parameters in C++11? In C++11,…
Bash has a -b test to test whether a file exists and is a block special file. -b file True if file exists and is a block special file. How to do this in Python? Python’s stat module provides the similar functions for the C standard APIs and macros underlining such as stat() and S_ISBLK()….
The problem is with ssh that makes a quoted string to more than one if there are spaces. For example, ssh user@host cmd “my string” The cmd on host will be executed like cmd my string rather than cmd “my string” It will only work if the string is escaped like ssh user@host cmd my…
In many text processing tasks, we often need to check if a given string starts with a specific substring. In this article, we will demonstrate how to achieve this using the std::string::compare() function from the C++ Standard Library. The compare() function has several overloads, but the one of interest for our purpose is: int compare(size_type…
How to split and iterate a string separated by a specific character in C++? For example, “a string separated by space” by ‘ ‘=> [“a”, “string”, “separated”, “by”, “space”] and “a,string,separated,by,comma” by ‘,’ => [“a”, “string”, “separated”, “by”, “comma”] C++ standard library’s getline() function can be used to build a function. getline() can accept a…
Admins usually need to generate some passwords for others, such as when creating a new user in a Linux system. How to generate a password in Shell on Linux? Several possible and short methods. Here, we generate a password of length 8. Using pwgen: $ pwgen 8 1 dao3PaW9 Password based on base64 (note that…
How to operator[] access element in a const map in C++? For example, the compiler will report error on this piece of code: #include <iostream> #include <string> #include <map> std::int64_t count(const std::map<std::string, std::int64_t>& map) { return map[“one”] + map[“two”]; } int main () { std::map<std::string, std::int64_t> map = { {“one”, 1}, {“two”, 2} }; std::cout…
Vim seems not indent C++11 lambas very well. How to make Vim indent C++11 lambdas correctly? For this following program, Vim indents it as #include <iostream> #include <string> #include <vector> #include <algorithm> int main () { std::vector<std::string> strs({“one”, “two”}); std::vector<std::string> newstrs; std::transform(strs.begin(), strs.end(), std::back_inserter(newstrs), [](const std::string& s) -> std::string { if (s == “one”) {…
How to iterate all dirs and files in a dir in C++? To open a dir, we can use opendir() to open a directory stream. DIR *opendir(const char *name); Then we can use readdir() to iterate the directory stream. struct dirent *readdir(DIR *dirp); Here is an example C++ program using these 2 library functions. #include…
How to get a path’s mtime in C++ on Linux? The path can be a file or a dir. You may call the standard library function lstat() for the file or dir under the path. int lstat(const char *pathname, struct stat *statbuf); From the returned stat struct, there is a field st_mtim which is the…
How to remove newline characters from a string in C++? For example, a string like line 1 line 3 line 4 should be converted to line 1line 3line 4 Method 1: use `erase()` and `remove()` In short, use this code snippet: input.erase(std::remove(input.begin(), input.end(), ‘\n’), input.end()); std::remove() shifts all elements that are equal to the value…
How to test whether a given path is a directory or a file in C++? For example, pathtype(“/”) –> “a dir” pathtype(“/tmp/file.txt”) –> “a file” # if there is a file file.txt pathtype(“/tmp/dir.txt”) –> “a dir” # if there is a dir named dir.txt The type of a file/dir can be found out using lstat()…