From 8e9058931b9138a208fef876b8a265121d54b512 Mon Sep 17 00:00:00 2001
From: Peter <peterr.00000@gmail.com>
Date: Fri, 17 Dec 2021 16:23:49 +0800
Subject: [PATCH] Day 17 solutions

---
 17/17-1.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 17/17-1.c

diff --git a/17/17-1.c b/17/17-1.c
new file mode 100644
index 0000000..50d0a3c
--- /dev/null
+++ b/17/17-1.c
@@ -0,0 +1,79 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+
+#define X_MIN 20
+#define X_MAX 30
+#define Y_MIN -10
+#define Y_MAX -5
+
+#define FACTOR 2 // Factor determines search domain
+
+typedef struct
+{
+    int x;
+    int y;
+} VECTOR2;
+
+bool in_target(VECTOR2 vector)
+{
+    return vector.x >= X_MIN && vector.x <= X_MAX && vector.y >= Y_MIN && vector.y <= Y_MAX;
+}
+bool past_target(VECTOR2 vector)
+{
+    return vector.x > X_MAX || vector.y < Y_MIN;
+}
+
+VECTOR2 add_vectors(VECTOR2 v1, VECTOR2 v2)
+{
+    VECTOR2 new = {v1.x + v2.x, v1.y + v2.y};
+    return new;
+}
+
+void print_vector(VECTOR2 v)
+{
+    printf("[%d,%d]\n", v.x, v.y);
+}
+
+bool try_velocity(VECTOR2 velocity, int *max_height)
+{
+    VECTOR2 position = {0, 0};
+    int max_height_l = 0;
+    while (true)
+    {
+        position = add_vectors(position, velocity);
+        if (position.y > max_height_l)
+            max_height_l = position.y;
+        // print_vector(position);
+        // UPDATE VELOCITY
+        velocity.y--;
+        velocity.x -= (velocity.x > 0 ? 1 : 0); // DRAG
+        if (in_target(position))
+        {
+            if (max_height_l > *max_height)
+                *max_height = max_height_l; // Required because FACTOR > 1
+            return true;
+        }
+        if (past_target(position))
+            return false;
+    }
+}
+
+int main(int argc, char const *argv[])
+{
+    // Really naive solution which iterates over many potential velocities,
+    // because the search domain is really small.
+    int max_height = 0;
+    int valid_iv = 0;
+    for (int i = 0; i < X_MAX * FACTOR; i++)
+    {
+        for (int j = -abs(Y_MIN * FACTOR); j < abs(Y_MIN * FACTOR); j++)
+        {
+            VECTOR2 velocity = {i, j};
+            if (try_velocity(velocity, &max_height))
+                valid_iv++;
+        }
+    }
+    printf("MAX_HEIGHT %d N_VALID_IV %d\n", max_height, valid_iv);
+    return 0;
+}