Freaks City

Six problems drawn from a competitive programming rating competition are analysed below. Every solution is accompanied by both C++ and Python implementations. Keep in mind that Python code may run slower and care should be taken with complexity constants. Problem 1 – Output a Digit Different from the Product Given two integers a and b, print an ...

In a binary matrix of size m x n, a subset of rows is considered "good" if, for every column, the sum of the elements in that column does not exceed half the size of the subset. Formally, if the subset conntains k rows, the sum of each column must be less than or equal to floor(k / 2). The goal is to return the indices of such a subse ...

Simple Factory Limitations Basic factory implementations often suffer from inflexibility when new types need to be added. Consider a web crawler system with different spider types: enum class CrawlerType { TEXT, IMAGE, }; class BasicSpiderFactory { public: static shared_ptr<Spider> CreateCrawler(CrawlerType type) { sw ...

Single header libraries often rely on a combination of standard header guards and specific implementation flags to separate declarations from definitions. While both use preprocessor directives, they solve diffferent problems at different stages of the compilation pipeline. 1. The Role of the Header Guard The primary purpose of a standard heade ...

Many users have encountered the avatar upload feature in Qt. Figure 1 should be familiar to most. This article demonstrates how to simulate a similar function, although it may not offer all the advanced features, it can fulfill basic requirements. Figure 1: QQ image upload Before diving into the functionality, I recommend reading a article on i ...

1. Concept and Definition of Inheritance Inheritance is a fundamental mechanism in object-oriented programming (OOP) that enables code reuse. It allows a new class (derived class) to extend an existing class (base class) by adding new features. Inheritance reflects the hierarchical structure of OOP and represents a cognitive process from simple ...

Problem A Given a snacks to distribute equally among b people. Snacks cannot be divided. Find the minimum number of additional snacks that need to be purchased. Solution Each person requires ceil(a/b) snacks. Therefore, the total snacks needed is ceil(a/b) * b. The additional snacks required is ceil(a/b) * b - a. int snacks, people; std::cin &g ...

Fundamentals of Greedy Strategies Greedy algorithms do not follow a rigid template. They essence lies in building a global optimum through a sequence of locally optimal choices. While formal proof of correctness is not mandatory for competitive programming (as long as the solution is accepted), a systematic approach helps: Break the problem in ...

The Problem with Shallow Copying A simple smart pointer implementation that lacks reference counting can suffer from a critical flaw known as the double-free error. This occurs when a copy of the pointer is made, causing both the original and the copy to point to the same underlying resource. When either of these pointers goes out of scope, it ...

Counting Palindromic Substrings This section addresses the problem of counting all palindromic substrings within a given string, similar to LeetCode problem 647. Problem Description Given a string s, determine and return the total count of palindromic substrings. A substring is a contiguous sequence of charcaters. A palindromic string reads the ...