library(tidyverse)
my_file <- here::here("2021", "data-2021-17.txt")
x <- readLines(my_file)
nums = str_extract_all(x, '-?\\d+')
x0 = as.integer(nums[[1]][1])
x1 = as.integer(nums[[1]][2])
y0 = as.integer(nums[[1]][3])
y1 = as.integer(nums[[1]][4])2021 Day 17
— Day 17: Trick Shot —
Send a probe into the ocean trench.
Find the initial velocity that causes the probe to reach the highest y position and still eventually be within the target area after any step. What is the highest y position it reaches on this trajectory?
We can probably try out all options and figure this out. Part two guess: the target area is multiplied by 100 or 1,000,000 and brute force becomes impossible.
# make a function so we can reuse program
cannonball <- function(v) {
pos = c(0,0)
max_y = -999
for (i in 1:1000) {
# move cannonball
pos[1] = pos[1] + v[1]
pos[2] = pos[2] + v[2]
if (pos[2] > max_y) {
max_y = pos[2]
}
# print for debug
# print(i)
# print(pos)
# print(v)
# test position
if (pos[1] >= x0 && pos[1] <= x1) {
if (pos[2] >= y0 && pos[2] <= y1) {
# found a good spot
break
}
}
# edit velocity
# x must always be positive for my target, I think
if (v[1] > 0) {
v[1] = v[1] - 1
} else {
v[1] = 0
}
v[2] = v[2] - 1
}
return(c(i, max_y))
}Use this function and see what we can find
# cannonball(c(14,7))
# has to be larger than 12, otherwise we don't get into the square
# 13: 5, 15; 6, 21;
# 14: 6, 21; 7, 28;
# Loop!
for (j in 10:30) {
max_y = 0
step = 0
for (k in 5:1000) {
res = cannonball(c(j, k))
# print(res)
if (res[1] < 1000) {
if (res[2] > max_y) {
max_y = res[2]
step = res[1]
}
}
}
print(c(j, step, max_y))
}[1] 10 0 0
[1] 11 0 0
[1] 12 0 0
[1] 13 300 11175
[1] 14 300 11175
[1] 15 300 11175
[1] 16 0 0
[1] 17 0 0
[1] 18 0 0
[1] 19 0 0
[1] 20 0 0
[1] 21 0 0
[1] 22 0 0
[1] 23 0 0
[1] 24 0 0
[1] 25 0 0
[1] 26 0 0
[1] 27 0 0
[1] 28 0 0
[1] 29 0 0
[1] 30 0 0— Part Two —
How many distinct initial velocity values cause the probe to be within the target area after any step?
all_count = 0
# Loop!
# Negatives!
for (j in 10:140) {
counter = 0
for (k in -200:1000) {
res = cannonball(c(j, k))
# print(res)
if (res[1] < 1000) {
counter = counter + 1
}
}
print(c(j, counter))
all_count = all_count + counter
}[1] 10 0
[1] 11 0
[1] 12 0
[1] 13 125
[1] 14 128
[1] 15 131
[1] 16 19
[1] 17 16
[1] 18 15
[1] 19 19
[1] 20 16
[1] 21 16
[1] 22 21
[1] 23 21
[1] 24 21
[1] 25 17
[1] 26 17
[1] 27 17
[1] 28 24
[1] 29 24
[1] 30 24
[1] 31 24
[1] 32 24
[1] 33 24
[1] 34 15
[1] 35 15
[1] 36 15
[1] 37 15
[1] 38 15
[1] 39 15
[1] 40 15
[1] 41 36
[1] 42 36
[1] 43 36
[1] 44 36
[1] 45 21
[1] 46 21
[1] 47 21
[1] 48 21
[1] 49 21
[1] 50 21
[1] 51 21
[1] 52 21
[1] 53 21
[1] 54 21
[1] 55 21
[1] 56 21
[1] 57 21
[1] 58 21
[1] 59 21
[1] 60 21
[1] 61 21
[1] 62 21
[1] 63 21
[1] 64 21
[1] 65 21
[1] 66 0
[1] 67 0
[1] 68 0
[1] 69 0
[1] 70 0
[1] 71 0
[1] 72 0
[1] 73 0
[1] 74 0
[1] 75 0
[1] 76 0
[1] 77 0
[1] 78 0
[1] 79 0
[1] 80 0
[1] 81 43
[1] 82 43
[1] 83 43
[1] 84 43
[1] 85 43
[1] 86 43
[1] 87 43
[1] 88 43
[1] 89 43
[1] 90 43
[1] 91 43
[1] 92 43
[1] 93 43
[1] 94 43
[1] 95 43
[1] 96 43
[1] 97 43
[1] 98 43
[1] 99 43
[1] 100 43
[1] 101 43
[1] 102 43
[1] 103 43
[1] 104 43
[1] 105 43
[1] 106 43
[1] 107 43
[1] 108 43
[1] 109 43
[1] 110 43
[1] 111 43
[1] 112 43
[1] 113 43
[1] 114 43
[1] 115 43
[1] 116 43
[1] 117 43
[1] 118 43
[1] 119 43
[1] 120 43
[1] 121 43
[1] 122 43
[1] 123 43
[1] 124 43
[1] 125 43
[1] 126 43
[1] 127 43
[1] 128 43
[1] 129 43
[1] 130 0
[1] 131 0
[1] 132 0
[1] 133 0
[1] 134 0
[1] 135 0
[1] 136 0
[1] 137 0
[1] 138 0
[1] 139 0
[1] 140 0print(all_count)[1] 3540