Project Euler/61
From charlesreid1
Problem Statement
This problem explores an extension of the concept of a triangular number, generated by the formula , to other shapes.
Exploring triangle, square, pentagonal, hexagonal, heptagonal, and octagonal numbers - numbers that are generated according to particular formulae:
Link: https://projecteuler.net/problem=61
Solution Technique
CURRENTLY UNSOLVED
Our solution technique is to generate a graph (for this, we use the Guava library).
We wish to find the sum of the ordered set of six cyclic 4-digit numbers for which each polygonal type, triangle/square/pentagonal/hexaongal,/heptagonal,octagonal, is represented by a different permutation of the digits (maintaining original order).
To do this, we create a graph, with each possible connection between a prefix and a suffix marked with an edge.
This results in a 6-partite graph, and we seek a path, a cycle, that passes through all 6 partitions.
crux (several years later)
The approach described above was sound, the implementation was logical, but the program just contained one significant, fatal bug: when we assembled the graph connecting four-digit numbers with shared first-two-digits and last-two-digits, we incorrectly implemented it to connect last-two-digits to last-two-digits. Change a % to a / and it worked okay.
Code
https://git.charlesreid1.com/cs/euler/src/branch/master/java/Problem061.java
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