## An Odyssey of Testing in Go

Why bother writing tests at all? It’s all about moving fast without breaking anything. This is a brief overview of the work we did on testing over the past half year in our team. With the help of CI, we significantly reduced the number of bugs and sped up the delivery of new features as we … Continue reading "An Odyssey of Testing in Go"

## Parse thrift in Go: the Antlr Way

thrift2interface is a small project I developed for auto generating go interfaces from thrift by Antlr4. This could be easily done by following the steps in Parsing with ANTLR 4 and Go with some extra efforts: Grammar The struct definition from the canonical Thrift.g4 may cause exceptions when generating Golang runtimes, this can be fixed … Continue reading "Parse thrift in Go: the Antlr Way"

## Polynomial Multiplication

Given two polynomials and of degree-bound : Multiply  and , we get the product with coefficients: Here  is also called the Convolution of  and  (denoted ). If we calculate  by multiplying each term in by each term in  and then combining terms with equal powers (exactly the old way we learnt in the junior high school), the time complexity would … Continue reading "Polynomial Multiplication"

## [Algorithm 101] Shortest Path Problem

In graph theory, the shortest path problem is the problem of finding a path between two vertices in a graph such that the sum of the weights of its constituent edges is minimized. Dijkstra’s algorithm For a given vertex called the source in a weighted connected graph, Dijkstra’s Algorithm can find the shortest paths to all the graph’s other vertices. This algorithm is applicable to both undirected … Continue reading "[Algorithm 101] Shortest Path Problem"

## Operational Transformation

Back to I was in a startup company two years ago, we were going to develop an online video chatroom over WebRTC with a collaborative real-time editor to share codes or thoughts for online interviews. Starting to build the editor from scratch seemed quite challenging for us at that time, so we chose etherpad-lite, an … Continue reading "Operational Transformation"

## [Algorithm 101] Topological Sorting

A directed acyclic graph (DAG) is not only necessary but also sufficient for topological sorting to be possible. DFS Perform a DFS traversal and note the order in which vertices become dead-ends (i.e., popped off the traversal stack). Reversing this order yields a solution to the topological sorting problem, provided, of course, no back edge has been encountered … Continue reading "[Algorithm 101] Topological Sorting"

## Matrix Multiplication: A Programmer’s Perspective

The problem find the nth fibonacci number(A000045) has an optimal solution: matrix multiplication. Similarly, the matrix representation of sequence An = An-1 + An-2 + An-3 (A000073) is: By using matrix multiplication, we can reduce the time complexity from O(n) to O(logn). In linear algebra textbooks, matrix multiplication is the composition of two linear functions. Suppose: Represent … Continue reading "Matrix Multiplication: A Programmer’s Perspective"

## Online Judge from Scratch(3) – Sandbox

This article consists of two parts: the sandbox for GCC and the sandbox for the compiled binary. the sandbox for GCC Essentially, our sandbox for GCC is a wrapper of GCC with a watchdog, just like the sandbox we designed for the Java compiler. However, there are more situations need to be considered carefully for GCC. In … Continue reading "Online Judge from Scratch(3) – Sandbox"