June 2018 Update

Task/Dinesmans-multiple-dwelling-problem/Lua/dinesmans-multiple-dwelling-problem.lua

@@ -0,0 +1,63 @@
+local wrap, yield = coroutine.wrap, coroutine.yield
+local function perm(n)
+    local r = {}
+    for i=1,n do r[i]=i end
+  return wrap(function()
+    local function swap(m)
+      if m==0 then
+        yield(r)
+      else
+        for i=m,1,-1 do
+          r[i],r[m]=r[m],r[i]
+          swap(m-1)
+          r[i],r[m]=r[m],r[i]
+        end
+      end
+    end
+    swap(n)
+  end)
+end
+
+local function iden(...)return ... end
+local function imap(t,f)
+  local r,fn = {m=imap, c=table.concat, u=table.unpack}, f or iden
+  for i=1,#t do r[i]=fn(t[i])end
+  return r
+end
+
+local tenants = {'Baker', 'Cooper', 'Fletcher', 'Miller', 'Smith'}
+
+local conds = {
+  'Baker  ~= TOP',
+  'Cooper ~= BOTTOM',
+  'Fletcher ~= TOP and Fletcher~= BOTTOM',
+  'Miller > Cooper',
+  'Smith + 1 ~= Fletcher and Smith - 1 ~= Fletcher',
+  'Cooper + 1 ~= Fletcher and Cooper - 1 ~= Fletcher',
+}
+
+local function makePredicate(conds, tenants)
+  return load('return function('..imap(tenants):c','..
+    ') return ' ..
+    imap(conds,function(c)
+      return string.format("(%s)",c)
+    end):c"and "..
+    " end ",'-',nil,{TOP=5, BOTTOM=1})()
+end
+
+local function solve (conds, tenants)
+  local try, pred, upk = perm(#tenants), makePredicate(conds, tenants), table.unpack
+  local answer = try()
+  while answer and not pred(upk(answer)) do answer = try()end
+  if answer then
+    local floor = 0
+    return imap(answer, function(person)
+        floor=floor+1;
+        return string.format(" %s lives on floor %d",tenants[floor],person)
+    end):c"\n"
+  else
+    return nil, 'no solution'
+  end
+end
+
+print(solve (conds, tenants))