[20260208] BOJ / P4 / 지민이의 테러 / 권혁준

khj20006/202602/08 BOJ P4 지민이의 테러.md

@@ -0,0 +1,67 @@
+```cpp
+#include <bits/stdc++.h>
+using namespace std;
+using ll = long long;
+using point = pair<ll, ll>;
+
+struct line {
+	point src, dest;
+	line(point a, point b) {
+		if (a > b) {
+			swap(a, b);
+		}
+		src = a, dest = b;
+	}
+};
+
+int N;
+vector<point> points;
+
+int ccw(point a, point b, point c) {
+	auto [ax, ay] = a;
+	auto [bx, by] = b;
+	auto [cx, cy] = c;
+	ll ret = (ax * by + bx * cy + cx * ay) - (ax * cy + bx * ay + cx * by);
+	return ret == 0 ? 0 : (ret > 0 ? 1 : -1);
+}
+
+bool line_intersection(line n1, line n2) {
+	auto [n1_src, n1_dest] = n1;
+	auto [n2_src, n2_dest] = n2;
+	int res1 = ccw(n1_src, n1_dest, n2_src) * ccw(n1_src, n1_dest, n2_dest);
+	int res2 = ccw(n2_src, n2_dest, n1_src) * ccw(n2_src, n2_dest, n1_dest);
+	if (res1 == 0 && res2 == 0) {
+		return n1_src <= n2_dest && n2_src <= n1_dest;
+	}
+	return res1 <= 0 && res2 <= 0;
+}
+
+bool point_in_polygon(point p) {
+	line n1 = line({ 1e9 + 1, 1e9 + 2 }, p);
+	bool ret = 0;
+	for (int i = 0; i < N; i++) {
+		line n2 = line(points[i], points[(i + 1) % N]);
+		if (ccw(p, n2.src, n2.dest) == 0 && n2.src <= p && p <= n2.dest) {
+			return true;
+		}
+		ret ^= line_intersection(n1, n2);
+	}
+	return ret;
+}
+
+int main() {
+	cin.tie(0)->sync_with_stdio(0);
+
+	cin >> N;
+	points.resize(N);
+	for (auto& [x, y] : points) {
+		cin >> x >> y;
+	}
+
+	for (int i = 0, x, y; i < 3; i++) {
+		cin >> x >> y;
+		cout << point_in_polygon({ x, y }) << '\n';
+	}
+
+}
+```