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Solving Advent of Code 2019-04 with R and JavaScript.

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

of Code, as it gives solutions for solving day 4.

[Disclaimer bis] I’m no JavaScript expert so this might not be the

perfect solution. TBH, that’s also the case for the R solution.

## About the JavaScript code

The JavaScript code has been written in the same RMarkdown as the R

code. It runs thanks to the `{bubble}`

package:

https://github.com/ColinFay/bubble

## Instructions

Find the instructions at: https://adventofcode.com/2019/day/4

## R solution

### Part one

```
test <- 156218:652527
library(magrittr)
cond <- function(vec){
splt <- strsplit(
as.character(vec),
"")[[1]] %>% as.numeric()
adj_eq <- (splt == dplyr::lag(splt))[-1]
incre <- (splt >= dplyr::lag(splt))[-1]
any(adj_eq) & all(incre)
}
vapply(test, cond, logical(1)) %>% sum()
```

```
## [1] 1694
```

### Part two

```
cond2 <- function(vec){
splt <- strsplit(
as.character(vec),
"")[[1]] %>% as.numeric()
adj_eq <- (splt == dplyr::lag(splt))[-1]
if (any(adj_eq)){
adj_eq <- any(table(splt) == 2)
}
incre <- (splt >= dplyr::lag(splt))[-1]
any(adj_eq) & all(incre)
}
vapply(test, cond2, logical(1)) %>% sum()
```

```
## [1] 1148
```

## JS solution

### Part one & Two

// Generating the array (from

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from)

```
const range = (start, stop, step = 1) => Array.from({ length: (stop - start) / step + 1}, (_, i) => start + (i * step));
var test = range(156218, 652527)
```

```
function lag(vec){
var res = [];
res.push(null);
for (var i = 0; i < vec.length - 1; i ++){
res.push(vec[i])
}
return res
}
function cond(vec){
var vec = vec.toString().split("").map(x => parseInt(x));
var laged = lag(vec);
var adj_eq = vec.map( (x, i) => x == laged[i] )
adj_eq.shift()
var adj_eq = adj_eq.some(z => z);
var incre = vec.map( (x, i) => x >= laged[i] )
incre.shift()
var incre = incre.every(z => z);
var all = [incre, adj_eq].every(z => z);
return all
}
```

```
test.map(cond).filter(v => v).length
```

```
## 1694
```

```
function table(vec){
var tbl = {}
vec.map(function(x){
if (tbl[x]){
tbl[x] = tbl[x] + 1;
} else {
tbl[x] = 1;
}
})
return tbl
}
function cond2(vec){
var vec = vec.toString().split("").map(x => parseInt(x));
var laged = lag(vec);
var adj_eq = vec.map( (x, i) => x == laged[i] )
adj_eq.shift()
var adj_eq = adj_eq.some(z => z);
if (adj_eq){
var tb = table(vec);
var res = [];
for (i in tb){
res.push(tb[i] == 2);
}
var adj_eq = res.some(x => x);
}
var incre = vec.map( (x, i) => x >= laged[i] );
incre.shift();
var incre = incre.every(z => z);
var all = [incre, adj_eq].every(z => z);
return all;
}
```

```
test.map(cond2).filter(v => v).length;
```

```
## 1148
```

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