update

poj/1569.myacm-triangles/main.cc

@@ -0,0 +1,79 @@
+#include <cmath>
+#include <cstdio>
+
+#define Vector Point
+
+using namespace std;
+
+const int N = 15;
+
+struct Point {
+  double x;
+  double y;
+  Point(double x = 0, double y = 0) : x(x), y(y){};
+} point[N];
+
+double operator^(const Vector &v1, const Vector &v2) {
+  return v1.x * v2.y - v1.y * v2.x;
+}
+
+Vector operator-(const Vector &v1, const Vector &v2) {
+  return Vector(v1.x - v2.x, v1.y - v2.y);
+}
+
+Vector operator+(const Vector &v1, const Vector &v2) {
+  return Vector(v1.x + v2.x, v1.y + v2.y);
+}
+
+Vector operator*(double k, const Vector &v) { return Vector(k * v.x, k * v.y); }
+
+int which_side(const Vector &v1, const Vector &v2) {
+  double res = v1 ^ v2;
+  if (res == 0) return 0;
+  if (0 < res) return 1;
+  return -1;
+}
+
+double area_of(const Vector &v1, const Vector &v2) { return fabs(v1 ^ v2) / 2; }
+
+int main() {
+  int n;
+  char p1, p2, p3, str[2];
+  while (scanf("%d", &n) != EOF) {
+    if (n == 0) break;
+    double max_area = 0;
+    for (int i = 0; i < n; i++)
+      scanf("%s %lf %lf", str, &point[i].x, &point[i].y);
+    for (int i = 0; i < n - 2; i++) {
+      for (int j = i + 1; j < n - 1; j++) {
+        for (int k = j + 1, side, l; k < n; k++) {
+          Point &a = point[i];
+          Point &b = point[j];
+          Point &c = point[k];
+          Vector v1 = c - a, v2 = a - b, v3 = b - c;
+          side = ((a - b) ^ (c - b)) < 0 ? -1 : 1;
+          for (l = 0; l < n; l++) {
+            if (l == i || l == j || l == k) continue;
+            Point &p = point[l];
+            int s1 = which_side(v1, p - a);
+            int s2 = which_side(v2, p - b);
+            int s3 = which_side(v3, p - c);
+            if ((s1 == 0 || s1 == side) && (s2 == 0 || s2 == side) &&
+                (s3 == 0 || s3 == side))
+              break;
+          }
+          if (l < n) continue;
+          double area = area_of(a - b, c - b);
+          if (max_area < area) {
+            max_area = area;
+            p1 = 'A' + i;
+            p2 = 'A' + j;
+            p3 = 'A' + k;
+          }
+        }
+      }
+    }
+    printf("%c%c%c\n", p1, p2, p3);
+  }
+  return 0;
+}