Initial data commit

Task/Sorting-algorithms-Pancake-sort/UNIX-Shell/sorting-algorithms-pancake-sort.sh

@@ -0,0 +1,93 @@
+#!/usr/bin/env bash
+main() {
+  local stack
+  local -i n m i
+  if (( $# )); then
+    stack=("$@")
+  else
+    stack=($(printf '%s\n' {0..9} | shuf))
+  fi
+  print_stack 0 "${stack[@]}"
+
+  # start by looking at whole stack
+  (( n = ${#stack[@]} ))
+
+  # keep going until we're all sorted
+  while (( n > 0 )); do
+
+    # shrink the stack until its bottom is not the right size
+    while  (( n > 0 && ${stack[n-1]} == n-1 )); do
+      (( n-=1 ))
+    done
+
+    # if we got to the top we're done
+    if (( n == 0 )); then
+      break
+    fi
+
+    # find the index of the largest pancake in the unsorted stack
+    m=0
+    for (( i=1; i < n-1; ++i )); do
+      if (( ${stack[i]} > ${stack[m]} )); then
+        (( m = i ))
+      fi
+    done
+
+    # if it's not on top, flip to get it there
+    if (( m > 0 )); then
+      stack=( $(flip "$(( m + 1 ))" "${stack[@]}") )
+      print_stack "$(( m + 1))" "${stack[@]}"
+    fi
+
+    # now flip the top to the bottom
+    stack=( $(flip "$n" "${stack[@]}" ) )
+    print_stack "$n" "${stack[@]}"
+
+    # and move up
+    (( n -= 1 ))
+  done
+  print_stack 0 "${stack[@]}"
+}
+
+# display the stack, optionally with brackets around a prefix
+print_stack() {
+  local prefix=$1
+  shift
+  if (( prefix )); then
+    printf '[%s' "$1"
+    if (( prefix > 1 )); then
+      printf ',%s' "${@:2:prefix-1}"
+    fi
+    printf ']'
+  else
+    printf ' '
+  fi
+  if (( prefix < $# )); then
+    printf '%s' "${@:prefix+1:1}"
+    if (( prefix+1 < $# )); then
+      printf ',%s' "${@:prefix+2:$#-prefix-1}"
+    fi
+  fi
+  printf '\n'
+}
+
+# reverse the first N elements of an array
+flip() {
+  local -i size end midpoint i
+  local stack temp
+  size=$1
+  shift
+  stack=( "$@" )
+  if (( size > 1 )); then
+    (( end = size - 1 ))
+    (( midpoint = size/2 + size % 2 ))
+    for (( i=0; i<midpoint; ++i )); do
+      temp=${stack[i]}
+      stack[i]=${stack[size-1-i]}
+      stack[size-1-i]=$temp
+    done
+  fi
+  printf '%s\n' "${stack[@]}"
+}
+
+main "$@"