langs a-z

Task/Hailstone-sequence/UNIX-Shell/hailstone-sequence-1.sh

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+#!/bin/bash
+# seq is the array genereated by hailstone
+# index is used for seq
+declare -a seq
+declare -i index
+
+# Create a routine to generate the hailstone sequence for a number
+hailstone () {
+  unset seq index
+  seq[$((index++))]=$((n=$1))
+  while [ $n -ne 1 ]; do
+    [ $((n % 2)) -eq 1 ] && ((n=n*3+1)) || ((n=n/2))
+    seq[$((index++))]=$n
+  done
+}
+
+# Use the routine to show that the hailstone sequence for the number 27
+# has 112 elements starting with 27, 82, 41, 124 and ending with 8, 4, 2, 1
+i=27
+hailstone $i
+echo "$i: ${#seq[@]}"
+echo "${seq[@]:0:4} ... ${seq[@]:(-4):4}"
+
+# Show the number less than 100,000 which has the longest hailstone
+# sequence together with that sequences length.
+# (But don't show the actual sequence)!
+max=0
+maxlen=0
+for ((i=1;i<100000;i++)); do
+  hailstone $i
+  if [ $((len=${#seq[@]})) -gt $maxlen ]; then
+    max=$i
+    maxlen=$len
+  fi
+done
+
+echo "${max} has a hailstone sequence length of ${maxlen}"