update

poj/1113.wall/main.cc

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+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <cstring>
+#include <vector>
+
+using namespace std;
+
+const int N = 1000;
+
+struct Point {
+  int x;
+  int y;
+  Point(int x = 0, int y = 0) : x(x), y(y) {}
+  bool operator<(const Point& that) const {
+    if (this->x == that.x) return this->y < that.y;
+    return this->x < that.x;
+  }
+  Point operator-(const Point& that) const {
+    return Point(this->x - that.x, this->y - that.y);
+  }
+  int operator^(const Point& that) const {
+    return this->x * that.y - this->y * that.x;
+  }
+} point[N];
+
+double dist(const Point& a, const Point& b) {
+  int dx = a.x - b.x;
+  int dy = a.y - b.y;
+  return sqrt((double)dx * dx + dy * dy);
+}
+
+int main() {
+  int n, l;
+  scanf("%d %d", &n, &l);
+  for (int i = 0; i < n; i++) scanf("%d %d", &point[i].x, &point[i].y);
+  sort(point, point + n);
+  vector<Point> stack;
+  stack.push_back(point[0]);
+  stack.push_back(point[1]);
+  for (int i = 2; i < n; i++) {
+    Point& p = point[i];
+    while (1 < stack.size()) {
+      Point p1 = *(stack.end() - 1);
+      Point p2 = *(stack.end() - 2);
+      if (((p2 - p1) ^ (p - p2)) < 0)
+        stack.pop_back();
+      else
+        break;
+    }
+    stack.push_back(p);
+  }
+  double len = 0.;
+  Point pre = *(stack.begin());
+  vector<Point>::iterator it;
+  for (it = ++stack.begin(); it != stack.end(); ++it) {
+    len += dist(pre, *it);
+    pre = *it;
+  }
+  stack.clear();
+  stack.push_back(point[n - 1]);
+  stack.push_back(point[n - 2]);
+  for (int i = n - 3; 0 <= i; i--) {
+    Point& p = point[i];
+    while (1 < stack.size()) {
+      Point p1 = *(stack.end() - 1);
+      Point p2 = *(stack.end() - 2);
+      if (((p2 - p1) ^ (p - p2)) < 0)
+        stack.pop_back();
+      else
+        break;
+    }
+    stack.push_back(p);
+  }
+  pre = *(stack.begin());
+  for (it = ++stack.begin(); it != stack.end(); ++it) {
+    len += dist(pre, *it);
+    pre = *it;
+  }
+  printf("%.0lf\n", len + acos(-1.) * l * 2);
+  return 0;
+}