Add BFS.lua

learning-lua/algo/BFS-tests.lua

@@ -0,0 +1,49 @@
+local BFS = require "algo.BFS"
+local Graph = require "algo.Graph"
+
+local function load_input(input)
+  local G = Graph:new()
+  for _, edge in ipairs(input) do
+    local from, to, cost = edge:match('(%w-)%-(%w+)=(%d+)')
+    G:add(from, to, cost)
+  end
+  return G
+end
+
+local function tim_test()
+  print("BFS tim_test...")
+  local input<const> = {'s-v=1', 's-w=4', 'v-w=2', 'v-t=6', 'w-t=3'}
+  local src<const> = 's'
+  local G = load_input(input)
+  local level_counts = {}
+  for from, to, weight, level in BFS:new(G, src):iterate() do
+    level_counts[level] = level_counts[level] or 0
+    level_counts[level] = level_counts[level] + 1
+    print(string.format("%d: %s-%s=%d", level, from, to, weight))
+  end
+  assert(level_counts[1] == 2)
+  assert(level_counts[2] == 3)
+  assert(level_counts[3] == 1)
+end
+
+local function scott_moura_test()
+  print("BFS scott_moura_test ... ")
+  local input<const> = {'A-B=2', 'A-C=4', 'A-D=4', 'B-F=6', 'C-F=5', 'C-E=7', 'C-D=1', 'D-E=5', 'D-H=11', 'E-G=3',
+                        'E-H=4', 'F-H=5', 'F-G=2', 'F-E=1', 'G-H=2'}
+  local src<const> = 'A'
+  local level_counts = {}
+  local G = load_input(input)
+  for from, to, weight, level in BFS:new(G, src):iterate() do
+    level_counts[level] = level_counts[level] or 0
+    level_counts[level] = level_counts[level] + 1
+    print(string.format("%d: %s-%s=%d", level, from, to, weight))
+  end
+  assert(level_counts[1] == 3)
+  assert(level_counts[2] == 6)
+  assert(level_counts[3] == 12)
+  assert(level_counts[4] == 10)
+  assert(level_counts[5] == 3)
+end
+
+tim_test()
+scott_moura_test()

learning-lua/algo/BFS.lua

@@ -0,0 +1,47 @@
+local Graph = require "algo.Graph"
+local Queue = require "algo.Queue"
+local BFS = {}
+local E = {}
+
+local function _iterate(bfs)
+  local q = Queue:new()
+  local level = 0
+  local from = bfs.src_vertex
+  repeat
+    local vertex = bfs.graph:vertex(from)
+    level = level + 1
+    for to, weight in vertex:outgoings() do
+      coroutine.yield(from, to, weight, level)
+      q:enqueue{to, weight, level, from}
+    end
+    local item = (q:dequeue() or E)
+    from, level = item[1], item[3]
+  until not from or from == bfs.src_vertex
+end
+
+function BFS:iterate()
+  return coroutine.wrap(function()
+    _iterate(self)
+  end)
+end
+
+function BFS:class(o)
+  setmetatable(o, BFS)
+  BFS.__index = BFS
+  return o
+end
+
+---@param G (table) graph
+---@param src (any) source vertex
+function BFS:new(G, src)
+  assert(G, "Missing Graph")
+  assert(Graph.isGraph(G), "G must be a graph object")
+  assert(src, "Missing source vertex")
+  assert(G:vertex(src), "Source vertex not found in graph")
+  return BFS:class{
+    graph = G,
+    src_vertex = src
+  }
+end
+
+return BFS