2021 Day 01

2021/01/README.md

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+# 2021 Day 01: Sonar Sweep
+Copyright (c) Eric Wastl
+#### [Direct Link](https://adventofcode.com/2021/day/01)
+
+## Part 1
+
+As the submarine drops below the surface of the ocean, it automatically performs a sonar sweep of the nearby sea floor. On a small screen, the sonar sweep report (your puzzle input) appears: each line is a measurement of the sea floor depth as the sweep looks further and further away from the submarine.
+
+For example, suppose you had the following report:
+
+```
+199
+200
+208
+210
+200
+207
+240
+269
+260
+263
+```
+
+This report indicates that, scanning outward from the submarine, the sonar sweep found depths of `199`, `200`, `208`, `210`, and so on.
+
+The first order of business is to figure out how quickly the depth increases, just so you know what you're dealing with - you never know if the keys will get carried into deeper water by an ocean current or a fish or something.
+
+To do this, count **the number of times a depth measurement increases** from the previous measurement. (There is no measurement before the first measurement.) In the example above, the changes are as follows:
+
+```
+199 (N/A - no previous measurement)
+200 (increased)
+208 (increased)
+210 (increased)
+200 (decreased)
+207 (increased)
+240 (increased)
+269 (increased)
+260 (decreased)
+263 (increased)
+```
+
+In this example, there are **`7`** measurements that are larger than the previous measurement.
+
+**How many measurements are larger than the previous measurement?**
+
+## Part 2
+
+Considering every single measurement isn't as useful as you expected: there's just too much noise in the data.
+
+Instead, consider sums of a **three-measurement sliding window**. Again considering the above example:
+
+```
+199  A      
+200  A B    
+208  A B C  
+210    B C D
+200  E   C D
+207  E F   D
+240  E F G  
+269    F G H
+260      G H
+263        H
+```
+
+Start by comparing the first and second three-measurement windows. The measurements in the first window are marked `A` (`199`, `200`, `208`); their sum is `199 + 200 + 208 = 607`. The second window is marked `B` (`200`, `208`, `210`); its sum is `618`. The sum of measurements in the second window is larger than the sum of the first, so this first comparison **increased**.
+
+Your goal now is to count **the number of times the sum of measurements in this sliding window increases** from the previous sum. So, compare `A` with `B`, then compare `B` with `C`, then `C` with `D`, and so on. Stop when there aren't enough measurements left to create a new three-measurement sum.
+
+In the above example, the sum of each three-measurement window is as follows:
+
+```
+A: 607 (N/A - no previous sum)
+B: 618 (increased)
+C: 618 (no change)
+D: 617 (decreased)
+E: 647 (increased)
+F: 716 (increased)
+G: 769 (increased)
+H: 792 (increased)
+```
+
+In this example, there are **`5`** sums that are larger than the previous sum.
+
+Consider sums of a three-measurement sliding window. **How many sums are larger than the previous sum?**