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308 votes
Accepted

Dijkstra path finding in C# is 15x slower than C++ version

First of all, you should run the FindPath method a couple of times before measuring, to give the C# runtime a chance to optimize the code. ...
mordecai154's user avatar
  • 2,146
53 votes

Dijkstra path finding in C# is 15x slower than C++ version

For the moment, I'm ignoring the C# code (and its speed), and reviewing the C++ code for ways it might be open to improvement in readability (but with a decent compiler, what I'm suggesting shouldn't ...
Jerry Coffin's user avatar
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15 votes
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Find the correct path through a 5 x 5 grid (coderbyte 'Correct path')

Unnecessary Import numpy is not required for this challenge. You are using none of its special capabilities. The following: ...
AJNeufeld's user avatar
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13 votes
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Shortest Path For Google Foobar (Prepare The Bunnies Escape)

Basically you need a breadth-first search with a minor tweak: each node represents a cell in the grid (x- and y-coordinates), each node knows its "saldo" (how many walls it may penetrate). What ...
coderodde's user avatar
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13 votes
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Python program to find a word ladder transforming "four" to "five"

By performing recursion, you are performing a depth-first search of four-letter words. However, this task involves finding a shortest path, and shortest-path problems are generally better done using ...
200_success's user avatar
11 votes

Dijkstra path finding in C# is 15x slower than C++ version

The multidimensional array might be the weakness of the C# implementation. Try using jagged arrays that are faster though not so easy to use. You can read more about it in What are the differences ...
t3chb0t's user avatar
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11 votes
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BFS shortest path for Google Foobar challenge "Prepare the Bunnies' Escape"

The algorithm in the post is to iterate over the walls, and for each wall, to remove that wall from the maze, and then solve the maze using breadth-first-search. If the maze is \$n×n\$, then there ...
Gareth Rees's user avatar
  • 49.6k
11 votes

Bellman-Ford optimisation in C

for (uint _ = 0; _ < nb_nodes - 1; _++) Maybe this was python code translated into C?!? Repect the norms of the community. Even though ...
J_H's user avatar
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9 votes
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BFS shortest path for Google Foobar "Prepare the Bunnies' Escape"

One problem might be your custom Queue class. The list you use as underlying data structure has O(n) behaviour for ...
Graipher's user avatar
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9 votes

Dijkstra path finding in C# is 15x slower than C++ version

More speed for both C++ and C# Revisiting an older question. While reading this question and its already very good answers the ...
Oliver Schönrock's user avatar
9 votes
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Graph puzzle resolver

...
Peter Taylor's user avatar
  • 24.1k
9 votes
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Implementation of A* algorithm in C++

Euclidean distance is used to calcualte the cost from current node to goal The code implements Manhattan distance, so the comment is wrong, or perhaps the code is wrong, but in any case it doesn't ...
user555045's user avatar
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9 votes

Optimizing Python BFS Code

I have only a couple of nitpicks: Nitpick 1 while len(queue) > 0: You can write just as: while queue: Nitpick 2 Instead of ...
coderodde's user avatar
  • 28.9k
8 votes

Dijkstra path finding in C# is 15x slower than C++ version

The worst problem is probably the use of the SortedSet collection. In my experience, the Sorted* collections are rarely what you ...
Ark-kun's user avatar
  • 181
8 votes

Compute shortest path in undirected graph

Intro code: There's a lot of "instant fail"s here: Include only the headers you need! Debugging macros are probably not acceptable for something like this. We can step through in a ...
user673679's user avatar
  • 11.8k
7 votes
Accepted

Dijkstra's algorithm in C99

Generally the variable and function naming is clear and makes the code easier to read. If this program is for a first or second year computer science class it's really very good. If you are new to C ...
pacmaninbw's user avatar
  • 24k
7 votes

Maze solver and generator in Python

Some notes to your coding styles (different from PEP 8 — Style Guide for Python Code and others): ...
MarianD's user avatar
  • 1,876
7 votes
Accepted

Maze solver and generator in Python

Just reviewing generator.py. 1. Review There are no docstrings. What do these functions do? What arguments do they take? What do they return? "verticies" is a typo for "vertices". There's repetitive ...
Gareth Rees's user avatar
  • 49.6k
7 votes
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A* Algorithm in C# for pathfinding 2D tile grid

There is a lot of code here, so there is a lot to say; no way I'll covered everything! I'll do the easy things first, and then assume lots of them before we look at the algorithm. Style Usually C#ers ...
VisualMelon's user avatar
  • 7,431
7 votes
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Fastest path on a snakes and ladders board

Don't use mutable default arguments. If you need to default to a list then default to None and then change to an empty list. Take the following example code: <...
Peilonrayz's user avatar
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7 votes

Implementation of Dijkstra's algorithm in Python

[x for x in range(1, 1001)] can be written as just list(range(1, 1001)). It would be good to give that ...
Carcigenicate's user avatar
7 votes
Accepted

Optimizing Python BFS Code

current = queue.pop() What this actually does, which perhaps you did not notice, is remove the last element of the list. So the queue is really a stack, and ...
user555045's user avatar
  • 10.1k
6 votes

2D grid Hamiltonian path puzzle solver

1. Review Code is easier to test (and measure the performance) if it's organized into functions or classes. In this case you have persistent data (W, ...
Gareth Rees's user avatar
  • 49.6k
6 votes

Find the correct path through a 5 x 5 grid (coderbyte 'Correct path')

calcpath should be calc_path as per PEP8. This seems like it's a name decided on by the challenge, but I thought I'd mention it. ...
Carcigenicate's user avatar
6 votes
Accepted

Speeding up Dijkstra's algorithm

PEP-8 Violations Variables (unseenNodes, currentNode) should be snake_case, not ...
AJNeufeld's user avatar
  • 33.9k
6 votes
Accepted

A* (shortest path) with the ability to remove up to one wall

The high level approach What would be a good way of implementing the wall logic to be within the A* algorithm? I've tried to simply add a canRemove boolean to the Cell object (which is holding the ...
user555045's user avatar
  • 10.1k
6 votes

Bellman-Ford optimisation in C

A few pieces of advice you can consider: As far as I'm aware, documentation comments are conventionally immediately before the declaration, not between the signature and the body of the ...
Solomon Ucko's user avatar
  • 1,566
6 votes
Accepted

Multithreading a shortest path algorithm

Avoid redefining integer types I see types like sint and uint, I think somewhere you have lines like: ...
G. Sliepen's user avatar
  • 58.7k
5 votes

Shortest path via two intermediate points

The key reasons for the poor performance are: Representing queue as a list. This is slow because popping an item off the beginning of a list takes time ...
Gareth Rees's user avatar
  • 49.6k

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