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=begin
File: graph_bfs.rb
Created Time: 2024-04-25
Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
=end
require 'set'
require_relative './graph_adjacency_list'
require_relative '../utils/vertex'
### 廣度優先走訪 ###
def graph_bfs ( graph , start_vet )
# 使用鄰接表來表示圖，以便獲取指定頂點的所有鄰接頂點
# 頂點走訪序列
res = [ ]
# 雜湊集合，用於記錄已被訪問過的頂點
visited = Set . new ( [ start_vet ] )
# 佇列用於實現 BFS
que = [ start_vet ]
# 以頂點 vet 為起點，迴圈直至訪問完所有頂點
while que . length > 0
vet = que . shift # 佇列首頂點出隊
res << vet # 記錄訪問頂點
# 走訪該頂點的所有鄰接頂點
for adj_vet in graph . adj_list [ vet ]
next if visited . include? ( adj_vet ) # 跳過已被訪問的頂點
que << adj_vet # 只入列未訪問的頂點
visited . add ( adj_vet ) # 標記該頂點已被訪問
end
end
# 返回頂點走訪序列
res
end
### Driver Code ###
if __FILE__ == $0
# 初始化無向圖
v = vals_to_vets ( [ 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] )
edges = [
[ v [ 0 ] , v [ 1 ] ] ,
[ v [ 0 ] , v [ 3 ] ] ,
[ v [ 1 ] , v [ 2 ] ] ,
[ v [ 1 ] , v [ 4 ] ] ,
[ v [ 2 ] , v [ 5 ] ] ,
[ v [ 3 ] , v [ 4 ] ] ,
[ v [ 3 ] , v [ 6 ] ] ,
[ v [ 4 ] , v [ 5 ] ] ,
[ v [ 4 ] , v [ 7 ] ] ,
[ v [ 5 ] , v [ 8 ] ] ,
[ v [ 6 ] , v [ 7 ] ] ,
[ v [ 7 ] , v [ 8 ] ] ,
]
graph = GraphAdjList . new ( edges )
puts " \n 初始化後，圖為 "
graph . __print__
# 廣度優先走訪
res = graph_bfs ( graph , v . first )
puts " \n 廣度優先便利（ ） "
p vets_to_vals ( res )
end
