Data commit

Task/Four-is-magic/UNIX-Shell/four-is-magic.sh

@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+name_of() {
+  # return the English name for a numeric value
+  local -i n=$1
+
+  if (( n < 0 )); then
+    printf 'negative %s\n' "$(name_of $(( -n )))"
+    return 0
+  fi
+
+  # Names for numbers that fit in a bash integer
+  local -A names=([0]=zero [1]=one [2]=two [3]=three [4]=four [5]=five
+                  [6]=six [7]=seven [8]=eight [9]=nine [10]=ten [11]=eleven
+                  [12]=twelve [13]=thirteen [14]=fourteen [15]=fifteen
+                  [16]=sixteen [17]=seventeen [18]=eighteen [19]=nineteen
+                  [20]=twenty [30]=thirty [40]=forty [50]=fifty [60]=sixty
+                  [70]=seventy [80]=eighty [90]=ninety [100]=hundred
+                  [1000]=thousand [1000000]=million [1000000000]=billion
+                  [1000000000000]=trillion [1000000000000000]=quadrillion
+                  [1000000000000000000]=quintillion)
+
+  # The powers of 10 above 10, in descending order
+  local powers_of_10=($(printf '%s\n' "${!names[@]}" | sort -nr | grep '00$'))
+
+  # find the largest power of 10 that is smaller than n
+  local -i i=0
+  local -i p=${powers_of_10[i]}
+  while ((  p > n  && i < ${#powers_of_10[@]}-1 )); do
+    i=i+1
+    p=${powers_of_10[$i]}
+  done
+
+  # if we found one, split on it and construct quotient 'name' remainder
+  if (( n >= p )); then
+    local -i quotient=n/p
+    local -i remainder=n%p
+    local remname=
+    if (( remainder > 0 )); then
+        remname=$(name_of $remainder)
+    fi
+    printf '%s %s\n' "$(name_of $quotient)" "${names[$p]}${remname:+ $remname}"
+  elif (( n > 20 )); then
+    # things are a little different under 100, since the multiples of
+    # 10 have their own names
+    local -i remainder=n%10
+    local -i tens=n-remainder
+    local remname=
+    if (( remainder > 0 )); then
+      remname=-$(name_of $remainder)
+    fi
+    printf '%s\n' "${names[$tens]}${remname:+$remname}"
+  else
+    printf '%s\n' "${names[$n]}"
+  fi
+
+  return 0
+}
+
+# Convert numbers into the length of their names
+# Display the series of values in name form until
+# the length turns into four; then terminate with "four is magic."
+# Again, takes a second argument, this time a prefix, to
+# facilitate tail recursion.
+four_is_magic() {
+  local -i n=$1
+  local prefix=$2
+  local name=$(name_of $n)
+
+  # capitalize the first entry
+  if [[ -z $prefix ]]; then
+    name=${name^}
+  fi
+
+  # Stop at 4, otherwise count the length of the name and recurse
+  if (( $n == 4 )); then
+     printf '%s%s is magic.\n' "${prefix:+$prefix, }" "$name"
+  else
+     local -i len=${#name}
+     four_is_magic "$len" "${prefix:+$prefix, }$name is $(name_of $len)"
+  fi
+}