[20250205] BOJ / 플래3 / 달리기 코스 / 권혁준

khj20006/202502/05 BOJ P3 달리기 코스.md

@@ -0,0 +1,120 @@
+```java
+
+import java.util.*;
+import java.io.*;
+
+class Point{
+	long x,y;
+	Point(long x, long y){
+		this.x = x;
+		this.y = y;
+	}
+}
+
+class Main {
+
+	// IO field
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	static StringTokenizer st;
+
+	static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+	static int nextInt() {return Integer.parseInt(st.nextToken());}
+	static long nextLong() {return Long.parseLong(st.nextToken());}
+	static void bwEnd() throws Exception {bw.flush();bw.close();}
+
+	// Additional field
+	static Point[] arr;
+	static Point[] convexHull;
+
+
+	static int N;
+	static long ans = 0;
+
+	// positive : ccw
+	static int ccw(Point a, Point b, Point c) {
+		long res = (a.x*b.y + b.x*c.y + c.x*a.y) - (b.x*a.y + c.x*b.y + a.x*c.y);
+		if(res > 0) return 1;
+		if(res < 0) return -1;
+		return 0;
+	}
+
+	public static void main(String[] args) throws Exception {
+
+		input();
+
+		if(N <= 2) {
+			if(N == 1) bw.write("0");
+			else {
+				long dx = arr[0].x - arr[1].x;
+				long dy = arr[0].y - arr[1].y;
+				bw.write((dx*dx+dy*dy) + "\n");
+			}
+			bwEnd();
+			return;
+		}
+
+		constructConvexHull();
+
+		rotate();
+
+		bw.write(ans+"\n");
+
+		bwEnd();
+	}
+
+	static void input() throws Exception {
+		nextLine();
+		N = nextInt();
+		arr = new Point[N];
+		for(int i=0;i<N;i++) {
+			nextLine();
+			arr[i] = new Point(nextLong(), nextLong());
+		}
+	}
+
+	static void constructConvexHull() {
+
+		Arrays.sort(arr, (a,b) -> {
+			if(a.x==b.x) return (int)(a.y-b.y);
+			return (int)(a.x-b.x);
+		});
+		List<Point> lowerHull = new ArrayList<>();
+		List<Point> upperHull = new ArrayList<>();
+		for(Point p : arr) {
+			while(lowerHull.size()>1 && ccw(lowerHull.get(lowerHull.size()-2), lowerHull.get(lowerHull.size()-1), p) <= 0) lowerHull.remove(lowerHull.size()-1);
+			lowerHull.add(p);
+			while(upperHull.size()>1 && ccw(upperHull.get(upperHull.size()-2), upperHull.get(upperHull.size()-1), p) >= 0) upperHull.remove(upperHull.size()-1);
+			upperHull.add(p);
+		}
+
+		convexHull = new Point[lowerHull.size() + upperHull.size() - 2];
+		int idx = 0;
+		for(Point p : upperHull) convexHull[idx++] = p;
+		idx--;
+		for(int i=lowerHull.size()-1;i>0;i--) convexHull[idx++] = lowerHull.get(i);
+
+	}
+
+	static void rotate() {
+		int p = 1, sz = convexHull.length;
+		for(int i=0;i<sz;i++) {
+			long dx = convexHull[p%sz].x - convexHull[(i+1)%sz].x;
+			long dy = convexHull[p%sz].y - convexHull[(i+1)%sz].y;
+			ans = Math.max(ans, dist(convexHull[i],convexHull[p%sz]));
+			while(p < 2*sz && ccw(convexHull[i], convexHull[(i+1)%sz], new Point(convexHull[(p+1)%sz].x - dx, convexHull[(p+1)%sz].y - dy)) <= 0) {
+				p++;
+				ans = Math.max(ans, dist(convexHull[i],convexHull[p%sz]));
+				dx = convexHull[p%sz].x - convexHull[(i+1)%sz].x;
+				dy = convexHull[p%sz].y - convexHull[(i+1)%sz].y;
+			}
+		}
+	}
+
+	static long dist(Point a, Point b) {
+		return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);
+	}
+
+}
+
+```