WiP 2021 Day 17 using spaceship operator.

adventofcode/2021/day/17/trick_shot.cpp

@@ -0,0 +1,64 @@
+#include <cmath>
+#include <limits>
+#include <print>
+#include <utility>
+
+struct vec2 {
+    int x, y;
+
+    constexpr vec2& operator+=(const vec2& that) noexcept {
+        this->x += that.x;
+        this->y += that.y;
+        return *this;
+    }
+
+    constexpr void drag() noexcept {
+        switch(std::bit_cast<int8_t>(this->x <=> 0)) {
+            case -1:
+                this->x -= 1;
+                break;
+            case  0:
+                break;
+            case +1:
+                this->x += 1;
+        }
+    }
+};
+
+struct rect_area {
+    vec2 top_left, bot_right;
+
+    constexpr bool contains(const vec2& p) const noexcept {
+        return top_left.x <= p.x and p.x <= bot_right.x and
+            bot_right.y <= p.y and p.y <= top_left.y;
+    }
+};
+
+constexpr auto solve(rect_area const& target_area) {
+    std::pair<int, int> ans{std::numeric_limits<int>::min(), 0};
+    for (int Y = -200; Y <= 1000; Y++) for (int X = -600; X <= 1000; X++) {
+        const vec2 v0{X, Y};
+        vec2 p{0, 0}, v{v0};
+        int potential_max_y{std::numeric_limits<int>::min()}; 
+        for (;;) {
+            p += v;
+            v.drag();
+            v += {0, -1};
+            potential_max_y = std::max(potential_max_y, p.y);
+            if (target_area.contains(p)) {
+                ans.first = std::max(ans.first, potential_max_y);
+                ans.second++;
+                break;
+            }
+            if (p.y <= target_area.bot_right.y) break;
+        }
+    }
+    return ans;
+}
+
+int main() {
+    constexpr rect_area target_area{{102, -90}, {157, -146}};
+    //static_assert(solve(target_area) == std::make_pair(10585, 5247));
+    const auto answer_pair = solve(target_area);
+    std::print("Part one: {}\nPart two: {}\n", answer_pair.first, answer_pair.second); 
+}