Data commit

Task/Monty-Hall-problem/UNIX-Shell/monty-hall-problem.sh

@@ -0,0 +1,72 @@
+#!/bin/bash
+# Simulates the "monty hall" probability paradox and shows results.
+# http://en.wikipedia.org/wiki/Monty_Hall_problem
+# (should rewrite this in C for faster calculating of huge number of rounds)
+# (Hacked up by Éric Tremblay, 07.dec.2010)
+
+num_rounds=10 #default number of rounds
+num_doors=3 # default number of doors
+[ "$1" = "" ] || num_rounds=$[$1+0]
+[ "$2" = "" ] || num_doors=$[$2+0]
+
+nbase=1 # or 0 if we want to see door numbers zero-based
+num_win=0; num_lose=0
+
+echo "Playing $num_rounds times, with $num_doors doors."
+[ "$num_doors" -lt 3 ] && {
+  echo "Hey, there has to be at least 3 doors!!"
+  exit 1
+}
+echo
+
+function one_round() {
+  winning_door=$[$RANDOM % $num_doors ]
+  player_picks_door=$[$RANDOM % $num_doors ]
+
+  # Host leaves this door AND the player's first choice closed, opens all others
+  # (this WILL loop forever if there is only 1 door)
+  host_skips_door=$winning_door
+  while [ "$host_skips_door" = "$player_picks_door" ]; do
+    #echo -n "(Host looks at door $host_skips_door...) "
+    host_skips_door=$[$RANDOM % $num_doors]
+  done
+
+  # Output the result of this round
+  #echo "Round $[$nbase+current_round]: "
+  echo -n "Player chooses #$[$nbase+$player_picks_door]. "
+  [ "$num_doors" -ge 10 ] &&
+    # listing too many door numbers (10 or more) will just clutter the output
+    echo -n "Host opens all except #$[$nbase+$host_skips_door] and #$[$nbase+$player_picks_door]. " \
+  || {
+    # less than 10 doors, we list them one by one instead of "all except ?? and ??"
+    echo -n "Host opens"
+    host_opens=0
+    while [ "$host_opens" -lt "$num_doors" ]; do
+      [ "$host_opens" != "$host_skips_door" ] && [ "$host_opens" != "$player_picks_door" ] && \
+      echo -n " #$[$nbase+$host_opens]"
+      host_opens=$[$host_opens+1]
+    done
+    echo -n " "
+  }
+  echo -n "(prize is behind #$[$nbase+$winning_door]) "
+  echo -n "Switch from $[$nbase+$player_picks_door] to $[$nbase+$host_skips_door]: "
+  [ "$winning_door" = "$host_skips_door" ] && {
+    echo "WIN."
+    num_win=$[num_win+1]
+  } || {
+    echo "LOSE."
+    num_lose=$[num_lose+1]
+  }
+} # end of function one_round
+
+# ok, let's go
+current_round=0
+while [ "$num_rounds" -gt "$current_round" ]; do
+  one_round
+  current_round=$[$current_round+1]
+done
+
+echo
+echo "Wins (switch to remaining door):  $num_win"
+echo "Losses (first guess was correct): $num_lose"
+exit 0