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https://github.com/julienschmidt/n-queens
Optimized algorithm to find all solutions for the N-Queens-Problem in Java
https://github.com/julienschmidt/n-queens
challenge java n-queens nqueens nqueens-problem nqueens-solution
Last synced: 10 days ago
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Optimized algorithm to find all solutions for the N-Queens-Problem in Java
- Host: GitHub
- URL: https://github.com/julienschmidt/n-queens
- Owner: julienschmidt
- Created: 2012-12-09T20:46:30.000Z (almost 12 years ago)
- Default Branch: master
- Last Pushed: 2017-05-03T18:35:57.000Z (over 7 years ago)
- Last Synced: 2024-05-08T17:32:12.899Z (6 months ago)
- Topics: challenge, java, n-queens, nqueens, nqueens-problem, nqueens-solution
- Language: Java
- Homepage:
- Size: 8.79 KB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
N-Queens
========
Submitted version of my entry to the *N-Queens speed-challenge* as part of the lab class *Fundamentals of Programming* of my first semester at the Technical University of Munich.
Progress from trivial to fast
-----------------------------
Since this was the winning submission (in the category "non-threaded"), I added a [`progress` branch](https://github.com/JulienSchmidt/N-Queens/commits/progress) where you can relive my progress from the trivial algorithm to the optimized (fast) algoritm.
You can browse the changes here: [`progress`](https://github.com/JulienSchmidt/N-Queens/commits/progress)
Known bugs
----------
Many, many spelling errors :)
Bytecode
--------
I heavily optimized the code so it generates almost optimal byte code for the the chosen algorithmic approach.
Here is the byte code generated from the performance-critical function:
private static int findPos(int, int, int, int);
Code:
0: iconst_0
1: istore 4
3: iload_0
4: iload_1
5: iload_2
6: ior
7: iload_3
8: ior
9: iconst_m1
10: ixor
11: iand
12: istore 7
14: iload 7
16: ifle 78
19: iload 7
21: ineg
22: iload 7
24: iand
25: istore 5
27: iload_1
28: iload 5
30: ior
31: istore 6
33: iload 7
35: iload 5
37: ixor
38: istore 7
40: iload 6
42: iload_0
43: if_icmpge 72
46: iload 4
48: iload_0
49: iload 6
51: iload_2
52: iload 5
54: ior
55: iconst_1
56: iushr
57: iload_3
58: iload 5
60: ior
61: iconst_1
62: ishl
63: invokestatic #31 // Method findPos:(IIII)I
66: iadd
67: istore 4
69: goto 14
72: iinc 4, 1
75: goto 14
78: iload 4
80: ireturn