rename repo, subdir for yearly challenges

2020/day10/ex2.bash

@@ -0,0 +1,39 @@
+#!/bin/bash
+#
+# ex2.bash: Advent2020 game, day 10/game 2.
+
+CMD=${0##*/}
+shopt -s extglob
+
+declare -a numbers
+readarray -t numbers <<< "$(sort -nr)"
+numbers+=(0)
+((last=numbers[0]+3))
+numbers=("$last" "${numbers[@]}")
+size=${#numbers[@]}
+
+declare -a res
+for ((i=1; i<size; ++i)); do
+	res[$i]=0
+done
+res[0]=1
+
+for ((i=0; i<size; ++i)); do
+	cur=${numbers[i]}
+	r=${res[i]}
+
+	for j in 1 2 3; do
+		((next=i+j))
+		if ((next < size)); then
+			nval=${numbers[next]}
+			((diff=cur-nval))
+			if ((diff > 0 && diff <= 3)); then
+				((res[next]+=r))
+			fi
+		fi
+	done
+done
+
+printf "%s : size=%d res=%d\n" "$CMD" "$size" "${res[size-1]}"
+
+exit 0