## --- Day 5: Hydrothermal Venture ---

You come across a field of hydrothermal vents on the ocean floor! These vents constantly produce large, opaque clouds, so it would be best to avoid them if possible.

They tend to form in *lines*; the submarine helpfully produces a list of nearby lines of vents (your puzzle input) for you to review. For example:

```
0,9 -> 5,9
8,0 -> 0,8
9,4 -> 3,4
2,2 -> 2,1
7,0 -> 7,4
6,4 -> 2,0
0,9 -> 2,9
3,4 -> 1,4
0,0 -> 8,8
5,5 -> 8,2
```

Each line of vents is given as a line segment in the format `x1,y1 -> x2,y2`

where `x1`

,`y1`

are the coordinates of one end the line segment and `x2`

,`y2`

are the coordinates of the other end. These line segments include the points at both ends. In other words:

- An entry like
`1,1 -> 1,3`

covers points`1,1`

,`1,2`

, and`1,3`

. - An entry like
`9,7 -> 7,7`

covers points`9,7`

,`8,7`

, and`7,7`

.

For now, *only consider horizontal and vertical lines*: lines where either `x1 = x2`

or `y1 = y2`

.

So, the horizontal and vertical lines from the above list would produce the following diagram:

```
.......1..
..1....1..
..1....1..
.......1..
.112111211
..........
..........
..........
..........
222111....
```

In this diagram, the top left corner is `0,0`

and the bottom right corner is `9,9`

. Each position is shown as *the number of lines which cover that point* or `.`

if no line covers that point. The top-left pair of `1`

s, for example, comes from `2,2 -> 2,1`

; the very bottom row is formed by the overlapping lines `0,9 -> 5,9`

and `0,9 -> 2,9`

.

To avoid the most dangerous areas, you need to determine *the number of points where at least two lines overlap*. In the above example, this is anywhere in the diagram with a `2`

or larger - a total of

points.*5*

Consider only horizontal and vertical lines. *At how many points do at least two lines overlap?*