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Solving Advent of Code 2019-07 with R.

[Disclaimer] Obviously, this post contains a big spoiler about Advent

of Code, as it gives solutions for solving day 7.

## Instructions

Find the instructions at: https://adventofcode.com/2019/day/7

## R solution

```
vec <- scan("input7.txt", numeric(), sep = ",")
# Getting parse_opcode
source("intcode_helpers.R")
prog <- function(vec, inputs, pos = 1){
ipt_stat <- 1
stock <- 1
while (pos < length(vec)) {
c(op_code, one, two, three) %<-% parse_opcode( vec, pos )
if (op_code == 99) {
return(
list(
vec = vec,
res = res,
pos = pos,
code = 99,
processed = FALSE
)
)
}
if (op_code %in% 1:2){
if (op_code == 1) fun <- `+`
if (op_code == 2) fun <- `*`
vec[three] <- fun(one, two)
pos <- pos + 4
} else if (op_code == 3){
if (stock > length(inputs)){
return(
list(
vec = vec,
res = res,
pos = pos,
code = op_code,
processed = TRUE
)
)
}
if (ipt_stat == 1){
vec[ vec[pos + 1] + 1 ] <- inputs[1]
ipt_stat <- 2
} else {
vec[ vec[pos + 1] + 1 ] <- inputs[2]
}
pos <- pos + 2
stock <- stock + 1
} else if (op_code == 4){
res <- vec[vec[pos + 1] + 1]
pos <- pos + 2
} else if (op_code == 5){
if (one != 0){
pos <- two + 1
} else {
pos <- pos + 3
}
} else if (op_code == 6){
if (one == 0){
pos <- two + 1
} else {
pos <- pos + 3
}
} else if (op_code == 7){
if (one < two){
vec[three] <- 1
} else {
vec[three] <- 0
}
pos <- pos + 4
} else if (op_code == 8){
if (one == two){
vec[three] <- 1
} else {
vec[three] <- 0
}
pos <- pos + 4
}
}
return(
list(
vec = vec,
res = res,
pos = pos,
code = op_code,
processed = FALSE
)
)
}
res <- 0
comb <- expand.grid(0:4, 0:4, 0:4, 0:4, 0:4)
to_keep <- apply(comb, 1, function(x){
length(unique(x)) != length(x)
})
comb <- comb[!to_keep, ]
for (i in seq_len(nrow(comb))){
phase <- comb[i, ] %>% as.numeric()
start <- 0
for (j in seq_along(phase)){
start <- prog(vec, c(phase[j], start))$res
}
res[i] <- start
}
max(res)
```

```
## [1] 67023
```

### Part two

```
library(purrr)
```

```
##
## Attaching package: 'purrr'
## The following object is masked from 'package:magrittr':
##
## set_names
```

```
res <- 0
comb <- expand.grid(5:9, 5:9, 5:9, 5:9, 5:9)
to_keep <- apply(comb, 1, function(x){
length(unique(x)) != length(x)
})
comb <- comb[!to_keep, ]
for (i in seq_len(nrow(comb))){
phase <- comb[i, ] %>% as.numeric()
A <- prog(vec, c(phase[1], 0))
B <- prog(vec, c(phase[2], A$res))
C <- prog(vec, c(phase[3], B$res))
D <- prog(vec, c(phase[4], C$res))
E <- prog(vec, c(phase[5], D$res))
while(
map_lgl(
list(A, B, C, D, E),
"processed"
) %>% all()
){
A <- prog(A$vec, E$res, pos = A$pos)
B <- prog(B$vec, A$res, pos = B$pos)
C <- prog(C$vec, B$res, pos = C$pos)
D <- prog(D$vec, C$res, pos = D$pos)
E <- prog(E$vec, D$res, pos = E$pos)
}
res[i] <- E$res
}
max(res)
```

```
## [1] 7818398
```

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