4 files changed, 82 insertions, 0 deletions
diff --git a/src/2017/day3/README.md b/src/2017/day3/README.md
index e69de29..fcf7558 100644
--- a/src/2017/day3/README.md
+++ b/src/2017/day3/README.md
@@ -0,0 +1,40 @@
+--- Day 3: Spiral Memory ---
+You come across an experimental new kind of memory stored on an infinite two-dimensional grid.
+
+Each square on the grid is allocated in a spiral pattern starting at a location marked 1 and then counting up while spiraling outward. For example, the first few squares are allocated like this:
+
+17  16  15  14  13
+18   5   4   3  12
+19   6   1   2  11
+20   7   8   9  10
+21  22  23---> ...
+While this is very space-efficient (no squares are skipped), requested data must be carried back to square 1 (the location of the only access port for this memory system) by programs that can only move up, down, left, or right. They always take the shortest path: the Manhattan Distance between the location of the data and square 1.
+
+For example:
+
+Data from square 1 is carried 0 steps, since it's at the access port.
+Data from square 12 is carried 3 steps, such as: down, left, left.
+Data from square 23 is carried only 2 steps: up twice.
+Data from square 1024 must be carried 31 steps.
+How many steps are required to carry the data from the square identified in your puzzle input all the way to the access port?
+
+Your puzzle input is 312051.
+
+--- Part Two ---
+As a stress test on the system, the programs here clear the grid and then store the value 1 in square 1. Then, in the same allocation order as shown above, they store the sum of the values in all adjacent squares, including diagonals.
+
+So, the first few squares' values are chosen as follows:
+
+Square 1 starts with the value 1.
+Square 2 has only one adjacent filled square (with value 1), so it also stores 1.
+Square 3 has both of the above squares as neighbors and stores the sum of their values, 2.
+Square 4 has all three of the aforementioned squares as neighbors and stores the sum of their values, 4.
+Square 5 only has the first and fourth squares as neighbors, so it gets the value 5.
+Once a square is written, its value does not change. Therefore, the first few squares would receive the following values:
+
+147  142  133  122   59
+304    5    4    2   57
+330   10    1    1   54
+351   11   23   25   26
+362  747  806--->   ...
+What is the first value written that is larger than your puzzle input?
diff --git a/src/2017/day3/aoc.cpp b/src/2017/day3/aoc.cpp
index ed2d9d3..85c2aa4 100644
--- a/src/2017/day3/aoc.cpp
+++ b/src/2017/day3/aoc.cpp
@@ -1,5 +1,45 @@
 #include "aoc.h"
+#include <math.h>
 
 namespace aoc2017 {
 
+std::pair<int, int> circle(int t) {
+  int i = 1;
+  int j = 0;
+  while ((i * i) < t) {
+    i += 2;
+    j += 1;
+  }
+  return {j, i};
 }
+
+void middles(int i, int m[]) {
+  int x = i * i;
+  for (int a : {0, 1, 2, 3}) {
+    int n = x - i + 1;
+    m[a] = (n + x) / 2;
+    x = n;
+  }
+}
+
+int closest(int t, int m[]) {
+  int min{INT32_MAX};
+  for (int a : {0, 1, 2, 3}) {
+    int d = std::abs(t - m[a]);
+    if (d < min) {
+      min = d;
+    }
+  }
+  return min;
+}
+
+int day3(int target) {
+  auto p = circle(target);
+  int ms[4] = {0};
+  middles(p.second, ms);
+  // printf("%d -> %d %d %d %d\n", target, ms[0], ms[1], ms[2], ms[3]);
+  int d = closest(target, ms);
+  return d + p.first;
+}
+
+} // namespace aoc2017
diff --git a/src/2017/day3/aoc.h b/src/2017/day3/aoc.h
index 7aacc4c..be3159d 100644
--- a/src/2017/day3/aoc.h
+++ b/src/2017/day3/aoc.h
@@ -3,4 +3,5 @@
 
 namespace aoc2017 {
 
+int day3(int);
 }
diff --git a/src/2017/day3/input b/src/2017/day3/input
index e69de29..8b13789 100644
--- a/src/2017/day3/input
+++ b/src/2017/day3/input
@@ -0,0 +1 @@
+