breadth-first-search | 易学教程

How do I stop the breadth-first search using Boost Graph Library when using a custom visitor?

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问题 Say I found the node that meets my criteria and I need to stop the search. 回答1: The solution is to throw an exception of your known type - then catch it on the calling side. From the FAQ: How do I perform an early exit from an algorithm such as BFS? Create a visitor that throws an exception when you want to cut off the search, then put your call to breadth_first_search inside of an appropriate try/catch block. This strikes many programmers as a misuse of exceptions, however, much thought was

Time complexity/MySQL performance analysis

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问题 Set up(MySQL): create table inRelation( party1 integer unsigned NOT NULL, party2 integer unsigned NOT NULL, unique (party1,party2) ); insert into inRelation(party1,party2) values(1,2),(1,3),(2,3),(1,4),(2,5),(3,5),(1,6),(1,7),(2,7),(5,7); mysql> select * from inRelation a -> join inRelation b on a.party2=b.party1 -> join inRelation c on b.party2=c.party1 -> where a.party1=1 and c.party2=7; +--------+--------+--------+--------+--------+--------+ | party1 | party2 | party1 | party2 | party1 |

Counting the number of edges traversed in a Breadth First Search?

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问题 This is my bfs algorithim. I want to store the number of edges i traversed in the field edges, but I can't figure out where to place the variable to add one for each edge. I keep getting answers that are too long, so i think this is harder than simply incrementing edge. It should be noted that this is supposed to calculate the edges along the true path only, not the extra edges. public int distance(Vertex x, Vertex y){ Queue<Vertex> search = new LinkedList<Vertex>(); search.add(x); x.visited

Changing attribute of nodes during breadth first search in R

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问题 I have created a random (Erdos-Renyi) graph that has 100 nodes. I have set an attribute value for all 100 nodes as 0. I find the node with the maximum degree (the most neighbors), and change its attribute value from 0 to 1. Then, using the node as the root node, and another node as a second root node, I do a breadth first search (BFS) on the network. This is related to this question. I do the breadth first search like this: # BFS on the network bfs <- graph.bfs(graph, root = c(root_node, root

Finding all possible paths in graph

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问题 I'm looking for some algorithm which will help me find all possible paths in a graph. Everything I found so far is not fully satisfying. Let's imagine we have a graph (tree) like this one: And let's use some algorithm like Breadth-First Search or Depth-First Search . In return we'll get something like 1, 2, 4, (2), 5, (2), 6, (2), (1), 3, 7, 8, (7), 9 Which is how we go through this tree and this is not what I'm looking for. I'd love to get all paths, like: 1 1, 2 1, 2, 4 1, 2, 5 1, 2, 6 1, 3

explain the Haskell breadth first numbering code to traverse trees

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问题 I am reading this paper by Chris Okasaki; titled "Breadth-First Numbering: Lessons from a Small Exercise in Algorithm Design". A question is - how is the magic happening in the algorithm? There are some figures (e.g. figure 7 titled "threading the output of one level into the input of next level") Unfortunately, maybe it's only me, but that figure has completely baffled me. I don't understand how the threading happens at all? 回答1: Breadth first traversal means traversing levels of a tree one

Choose numbers which sum to zero

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There is N number of sets, each containing various number of integers, e.g.: (-2, -1, 0), (-1,4), (-2, 2, 3), (-3, -2, 4, 6), (-2) How to pick exactly one number from each set so that these N integers sum to zero? For example: -1, -1, 2, -2, 4, -2 Note there might be no solution or multiple (in which case it doesn't matter which one I choose). I was thinking that I can do breath-first search but was wondering if there are any other, preferably faster, ways to solve this. Let dp[i, j] = true iff we can make sum j using one number from each of the sets 1, 2, ..., i . dp[i, 0] = true for all i

How to use the BFS algorithm to keep only the outer points?

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问题 Let's say I have a 500x500 2D grid (from -250 to 250). Each cell of the grid has a certain value, from 0 to 100. What I've been trying to do is keep a list of all the cell with a value lower than 50 starting at the point (0, 0), but I would like not to keep all the points, but only the outer points (perimeter, bounds, a cell with a value lower than 50 that does not have 4 adjacent cells with a value lower than 50). The way I implemented the algorithm, I keep a list of all the points. How

Same result for two arrays of counters of different algorithms

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I'm trying to build up a program comparing number of strokes of algorithms BFS, DFS, A* (which has two heuristics) on a game of fifteen. My counter count the same result for the two arrays of counters of BFS and DFS and both A*. Yet, I'm using actually using four different arrays from a main (class Project) and I'm assigning four different variables for those strokes. The part of the code that isn't right is, to my mind, a while loop which explores the son of a vertice as far as possible (for BFS) or discovering each following nodes (for BFS). The difference, which is of the utmost importance,

Counting the number of edges traversed in a Breadth First Search?

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This is my bfs algorithim. I want to store the number of edges i traversed in the field edges, but I can't figure out where to place the variable to add one for each edge. I keep getting answers that are too long, so i think this is harder than simply incrementing edge. It should be noted that this is supposed to calculate the edges along the true path only, not the extra edges. public int distance(Vertex x, Vertex y){ Queue<Vertex> search = new LinkedList<Vertex>(); search.add(x); x.visited = true; while(!search.isEmpty()){ Vertex t = search.poll(); if(t == y){ return edges; } for(Vertex n: t