langs a-z

Task/Dinesmans-multiple-dwelling-problem/UNIX-Shell/dinesmans-multiple-dwelling-problem.sh

@@ -0,0 +1,71 @@
+#!/bin/bash
+
+NAMES=(Baker Cooper Fletcher Miller Smith)
+
+CRITERIA=(
+  'Baker    != TOP'
+  'Cooper   != BOTTOM'
+  'Fletcher != TOP'
+  'Fletcher != BOTTOM'
+  'Miller   >  Cooper'
+  '$(abs $(( Smith    - Fletcher )) ) > 1'
+  '$(abs $(( Fletcher - Cooper   )) ) > 1'
+)
+
+# Code below here shouldn't need to change to vary parameters
+let BOTTOM=0
+let TOP=${#NAMES[@]}-1
+
+# Not available as a builtin
+function abs {
+  let n=$1
+  if (( n < 0 )); then let n=-n; fi
+  echo "$n"
+}
+
+# Algorithm we use to iterate over the permutations
+# requires that we start with the array sorted lexically
+NAMES=($(printf "%s\n" "${NAMES[@]}" | sort))
+while true; do
+  # set each name to its position in the array
+  for (( i=BOTTOM; i<=TOP; ++i )); do
+    eval "${NAMES[i]}=$i"
+  done
+
+  # check to see if we've solved the problem
+  let solved=1
+  for criterion in "${CRITERIA[@]}"; do
+    if ! eval "(( $criterion ))"; then
+      let solved=0
+      break
+    fi
+  done
+  if (( solved )); then
+    echo "From bottom to top: ${NAMES[@]}"
+    break
+  fi
+
+  # Bump the names list to the next permutation
+  let j=TOP-1
+  while (( j >= BOTTOM )) && ! [[ "${NAMES[j]}" < "${NAMES[j+1]}" ]]; do
+    let j-=1
+  done
+  if (( j < BOTTOM )); then break; fi
+  let k=TOP
+  while (( k > j )) && [[ "${NAMES[k]}" < "${NAMES[j]}" ]]; do
+    let k-=1
+  done
+  if (( k <= j )); then break; fi
+  t="${NAMES[j]}"
+  NAMES[j]="${NAMES[k]}"
+  NAMES[k]="$t"
+  for (( k=1; k<=(TOP-j); ++k )); do
+    a=BOTTOM+j+k
+    b=TOP-k+1
+    if (( a < b )); then
+      t="${NAMES[a]}"
+      NAMES[a]="${NAMES[b]}"
+      NAMES[b]="$t"
+    fi
+  done
+done