+#!/bin/bash
+
+set -u
+set -e
+
+filename=${1:-small_grid.txt}
+
+exec 3<$filename
+
+declare -A asteroids
+declare -A cansee
+declare -A cantsee
+
+ln=0
+width=0
+while read -u 3 line; do
+ width=${#line}
+ for (( a=0; a<${#line}; a++ )); do
+ char=${line:$a:1}
+ if [ "${char}" == "#" ]; then
+ asteroids[$a,$ln]=0
+ fi
+ done
+ ln=$((ln+1))
+done
+
+debug_line() {
+ line="$@"
+ #echo "$line" >&2
+}
+
+get_vector() {
+ local x1=$1
+ local y1=$2
+ local x2=$3
+ local y2=$4
+
+ x_diff=$(($x1 - $x2))
+ y_diff=$(($y1 - $y2))
+
+ echo "$x_diff,$y_diff"
+}
+
+check_collision() {
+ # we want to know if vector2 is going to get in the way of vector1
+ local vector1=$1
+ local vector2=$2
+
+ debug_line Comparing: $vector1 $vector2
+
+ vector1_x=${vector1%,*}
+ vector1_y=${vector1#*,}
+ vector2_x=${vector2%,*}
+ vector2_y=${vector2#*,}
+
+ # potentially blocking asteroid
+ # first calculate the minimum x and y steps that are whole numbers
+ # min number first, we'll then halve it and work through the steps
+
+ # work out which asteroid is furthest from use
+ vector1_x_val=${vector1_x#-}
+ vector1_y_val=${vector1_y#-}
+ vector2_x_val=${vector2_x#-}
+ vector2_y_val=${vector2_y#-}
+
+ minimum_number=$vector2_x_val
+ if ( [ $vector2_x_val -gt $vector2_y_val ] && [ $vector2_y_val -gt 0 ] ) ||
+ [ $minimum_number -eq 0 ]; then
+ minimum_number=$vector2_y_val
+ fi
+
+ debug_line "Min number: $minimum_number"
+
+ minstep_x=$vector2_x
+ minstep_y=$vector2_y
+ for (( a=$minimum_number; a>0; a-- )); do
+ if [ $((vector2_x % $a)) -eq 0 ] && [ $((vector2_y % $a)) -eq 0 ]; then
+ minstep_x=$((vector2_x / $a))
+ minstep_y=$((vector2_y / $a))
+ break
+ fi
+ done
+ debug_line "Have minsteps: $minstep_x,$minstep_y"
+
+ # in all other cases, we're at least heading in the right direction
+ cur_x=$vector2_x
+ cur_y=$vector2_y
+
+ debug_line "Looking for: $vector1_x,$vector1_y"
+ debug_line "Start: $cur_x,$cur_y"
+
+ # from the starting point, add the min steps until we're past the other asteroid
+ while keep_going $cur_x $cur_y $minstep_x $minstep_y $vector1_x $vector1_y; do
+ cur_x=$((cur_x+$minstep_x))
+ cur_y=$((cur_y+$minstep_y))
+ debug_line "Step: $cur_x,$cur_y"
+ if [ $cur_x -eq $vector1_x ] && [ $cur_y -eq $vector1_y ]; then
+ debug_line echo "Collision!"
+ return 0
+ fi
+ done
+
+ return 1
+}
+
+keep_going() {
+ local cur_x=$1
+ local cur_y=$2
+ local minstep_x=$3
+ local minstep_y=$4
+ local ast_x=$5
+ local ast_y=$6
+
+ if [ $minstep_x -lt 0 ] && [ $cur_x -lt $ast_x ]; then
+ # past the asteroid, we missed
+ debug_line "stop cond 1"
+ return 1
+ elif [ $minstep_y -lt 0 ] && [ $cur_y -lt $ast_y ]; then
+ # past the asteroid, we missed
+ debug_line "stop cond 2"
+ return 1
+ elif [ $minstep_x -gt 0 ] && [ $cur_x -gt $ast_x ]; then
+ debug_line "stop cond 3"
+ return 1
+ elif [ $minstep_y -gt 0 ] && [ $cur_y -gt $ast_y ]; then
+ debug_line "stop cond 4"
+ return 1
+ fi
+
+ return 0
+}
+
+# we check for if the first asteroid is blocked viewing the second asteroid
+# by the third asteroid, if not we add 1 to it's total
+for asteroid in ${!asteroids[@]}; do
+#for asteroid in 9,0; do
+ ast1_x=${asteroid%,*}
+ ast1_y=${asteroid#*,}
+
+ for asteroid2 in ${!asteroids[@]}; do
+ #for asteroid2 in 4,5; do
+ if [ $asteroid2 == $asteroid ]; then
+ continue
+ fi
+ ast2_x=${asteroid2%,*}
+ ast2_y=${asteroid2#*,}
+
+ vector1=$(get_vector $ast1_x $ast1_y $ast2_x $ast2_y)
+
+ # if we've got a cached can't see, use it to continue the loop
+ if [ ${cantsee[$asteroid,$asteroid2]+a} ]; then
+ continue
+ fi
+
+ if ! [ ${cansee[$asteroid,$asteroid2]+a} ]; then # we already calculated this backwards
+ for asteroid3 in ${!asteroids[@]}; do
+ if [ $asteroid == $asteroid3 ] || [ $asteroid2 == $asteroid3 ]; then
+ continue
+ fi
+ ast3_x=${asteroid3%,*}
+ ast3_y=${asteroid3#*,}
+ debug_line "Checking for collision between $asteroid and $asteroid2 by $asteroid3"
+ vector2=$(get_vector $ast1_x $ast1_y $ast3_x $ast3_y)
+ if ( check_collision $vector1 $vector2 ); then
+ # path is blocked go on to next in outer loop
+ debug_line "We hit $asteroid3 when looking for $asteroid2 from $asteroid"
+ cantsee[$asteroid2,$asteroid]=1
+ cantsee[$asteroid,$asteroid2]=1
+ continue 2
+ fi
+ done
+ fi
+ # nothing blocked the view of asteroid2 from asteroid1
+ debug_line "Apparently $asteroid can set $asteroid2"
+ asteroids[$asteroid]=$((asteroids[$asteroid]+1))
+ cansee[$asteroid2,$asteroid]=1 # don't bother doing the expensive calculations on the return path
+ done
+done
+
+best_ast=
+best_count=0
+for asteroid in ${!asteroids[@]}; do
+ count=${asteroids[$asteroid]}
+ if [ $count -gt $best_count ]; then
+ best_count=$count
+ best_ast=$asteroid
+ fi
+ debug_line "$asteroid: ${asteroids[$asteroid]}"
+done
+
+echo "Best asteroid: $best_ast which can see $best_count asteroids"
+
+#echo -n "+"
+#printf "%.0s-" $(seq 1 $width)
+#echo "+"
+## redraw the board with numbers
+#for (( a=0; a<$ln; a++ )); do
+# echo -n "|"
+# for (( b=0; b<$width; b++ )); do
+# if [ ${asteroids[$b,$a]+a} ]; then
+# echo -n ${asteroids[$b,$a]}
+# else
+# echo -n "."
+# fi
+# done
+# echo "|"
+#done
+#echo -n "+"
+#printf "%.0s-" $(seq 1 $width)
+#echo "+"
projects / advent-of-code-2019.git / commitdiff