aboutsummaryrefslogtreecommitdiff
path: root/2021
diff options
context:
space:
mode:
Diffstat (limited to '2021')
-rwxr-xr-x2021/day17/day17bin0 -> 99088 bytes
-rw-r--r--2021/day17/day17.cpp87
-rw-r--r--2021/day17/makefile2
3 files changed, 89 insertions, 0 deletions
diff --git a/2021/day17/day17 b/2021/day17/day17
new file mode 100755
index 0000000..d941d78
--- /dev/null
+++ b/2021/day17/day17
Binary files differ
diff --git a/2021/day17/day17.cpp b/2021/day17/day17.cpp
new file mode 100644
index 0000000..305900a
--- /dev/null
+++ b/2021/day17/day17.cpp
@@ -0,0 +1,87 @@
+#include <iostream>
+#include <string>
+#include <vector>
+#include <map>
+
+// -- notes
+// if vy(0) > 0 the trajectory always reaches y=0 at time t
+// and vy(t) = -vy(0), vy(t+1) = -vy(0)-1
+// sum {i:1..n} (n) = ((n)(n+1))/2
+// triangle = { i in N | exist an n in N s.t. i = sum(n) }
+// if probe reaches y=0 with vx(t)=0, vx(0) is in triangle
+// so for every vx(0) in sumn and sum(vx(0)) in target
+// get the largest vy(t) in target
+// this approach only works if vy(0)>0
+
+std::vector<int> parse_range(std::string raw) {
+ std::vector<int> range;
+ std::string nolabel = raw.substr(2);
+ auto dotdot = nolabel.find("..");
+ std::string r = nolabel.substr(0, dotdot);
+ std::string l = nolabel.substr(dotdot+2);
+ range.push_back(std::stoi(r));
+ range.push_back(std::stoi(l));
+ return range;
+}
+
+int get_trig (int n) {
+ return ((n)*(n+1))/2;
+}
+
+int validate (int vx, int vy, std::vector<int> range, int maxt) {
+ int x = 0, y = 0;
+ for (int t=0; t<maxt; t++) {
+ x += vx; y += vy;
+ if (vx > 0) vx--;
+ vy--;
+ if (range[0] <= x && x <= range[1])
+ if (range[2] <= y && y <= range[3])
+ return 1;
+ if (y < range[2]) return 0;
+ }
+ return 0;
+}
+
+int main (int argc, char *argv[]) {
+ std::string raw = std::string({ argv[1] });
+ std::string nolabel = raw.substr(13);
+ auto comma = nolabel.find(", ");
+ std::string rangex = nolabel.substr(0, comma);
+ std::string rangey = nolabel.substr(comma+2);
+ auto range = parse_range(rangex);
+ auto ry = parse_range(rangey);
+ range.insert(std::end(range), std::begin(ry), std::end(ry));
+ // range is x1, x2, y1, y2
+
+ std::map<int, int> triangles {};
+ for (int i=0; i<100; i++) {
+ triangles[get_trig(i)] = i;
+ }
+
+ int vx = 0;
+ int vy = 0;
+ for (int i=range[0]; i<range[1]; i++) {
+ if (triangles.contains(i)) {
+ for (int j=range[2]; j<range[3]; j++) {
+ if (-j > vy) {
+ vy = -j-1;
+ vx = triangles[i];
+ }
+ }
+ }
+ }
+
+ std::cout << "velocity: vx=" << vx << ", vy=" << vy << std::endl;
+ std::cout << "max height: " << get_trig(vy) << std::endl;
+
+ int sum = 0;
+ for (int i=0; i<range[1]*2; i++) {
+ for (int j=range[2]; j<vy+1; j++) {
+ sum += validate(i, j, range, 1000);
+ }
+ }
+
+ std::cout << "total intial velocities: " << sum << std::endl;
+
+ return 0;
+}
diff --git a/2021/day17/makefile b/2021/day17/makefile
new file mode 100644
index 0000000..293f3ea
--- /dev/null
+++ b/2021/day17/makefile
@@ -0,0 +1,2 @@
+all day17.cpp:
+ g++ -std=c++20 day17.cpp -o day17