Data commit

Task/Monty-Hall-problem/Julia/monty-hall-problem-1.julia

@@ -0,0 +1,22 @@
+using Printf
+
+function play_mh_literal{T<:Integer}(ncur::T=3, ncar::T=1)
+    ncar < ncur || throw(DomainError())
+    curtains = shuffle(collect(1:ncur))
+    cars = curtains[1:ncar]
+    goats = curtains[(ncar+1):end]
+    pick = rand(1:ncur)
+    isstickwin = pick in cars
+    deleteat!(curtains, findin(curtains, pick))
+    if !isstickwin
+        deleteat!(goats, findin(goats, pick))
+    end
+    if length(goats) > 0 # reveal goat
+        deleteat!(curtains, findin(curtains, shuffle(goats)[1]))
+    else # no goats, so reveal car
+        deleteat!(curtains, rand(1:(ncur-1)))
+    end
+    pick = shuffle(curtains)[1]
+    isswitchwin = pick in cars
+    return (isstickwin, isswitchwin)
+end

Task/Monty-Hall-problem/Julia/monty-hall-problem-2.julia

@@ -0,0 +1,11 @@
+function play_mh_clean{T<:Integer}(ncur::T=3, ncar::T=1)
+    ncar < ncur || throw(DomainError())
+    pick = rand(1:ncur)
+    isstickwin = pick <= ncar
+    pick = rand(1:(ncur-2))
+    if isstickwin # remove initially picked car from consideration
+        pick += 1
+    end
+    isswitchwin = pick <= ncar
+    return (isstickwin, isswitchwin)
+end

Task/Monty-Hall-problem/Julia/monty-hall-problem-3.julia

@@ -0,0 +1,44 @@
+function mh_results{T<:Integer}(ncur::T, ncar::T,
+                                nruns::T, play_mh::Function)
+    stickwins = 0
+    switchwins = 0
+    for i in 1:nruns
+        (isstickwin, isswitchwin) = play_mh(ncur, ncar)
+        if isstickwin
+            stickwins += 1
+        end
+        if isswitchwin
+            switchwins += 1
+        end
+    end
+    return (stickwins/nruns, switchwins/nruns)
+end
+
+function mh_analytic{T<:Integer}(ncur::T, ncar::T)
+    stickodds = ncar/ncur
+    switchodds = (ncar - stickodds)/(ncur-2)
+    return (stickodds, switchodds)
+end
+
+function show_odds{T<:Real}(a::T, b::T)
+    @sprintf "   %.1f   %.1f     %.2f" 100.0*a 100*b 1.0*b/a
+end
+
+function show_simulation{T<:Integer}(ncur::T, ncar::T, nruns::T)
+    println()
+    print("Simulating a ", ncur, " door, ", ncar, " car ")
+    println("Monty Hall problem with ", nruns, " runs.\n")
+
+    println("   Solution   Stick  Switch  Improvement")
+
+    (a, b) = mh_results(ncur, ncar, nruns, play_mh_literal)
+    println(@sprintf("%10s: ", "Literal"), show_odds(a, b))
+
+    (a, b) = mh_results(ncur, ncar, nruns, play_mh_clean)
+    println(@sprintf("%10s: ", "Clean"), show_odds(a, b))
+
+    (a, b) = mh_analytic(ncur, ncar)
+    println(@sprintf("%10s: ", "Analytic"), show_odds(a, b))
+    println()
+    return nothing
+end

Task/Monty-Hall-problem/Julia/monty-hall-problem-4.julia

@@ -0,0 +1,3 @@
+for i in 3:5, j in 1:(i-2)
+    show_simulation(i, j, 10^5)
+end