POJ 2007 Scrambled Polygon 凸包点排序逆时针输出
2013-11-14 20:19
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题意:如题
用Graham,直接就能得到逆时针的凸包,找到原点输出就行了,赤果果的水题~
代码:
用Graham,直接就能得到逆时针的凸包,找到原点输出就行了,赤果果的水题~
代码:
/* * Author: illuz <iilluzen[at]gmail.com> * Blog: http://blog.csdn.net/hcbbt * File: poj2007.cpp * Create Date: 2013-11-14 18:55:37 * Descripton: convex hull */ #include <cstdio> #include <cstring> #include <cmath> #include <algorithm> using namespace std; #define sqr(a) ((a) * (a)) #define dis(a, b) sqrt(sqr(a.x - b.x) + sqr(a.y - b.y)) const int MAXN = 110; const double PI = acos(-1.0); struct Point { int x; int y; Point(double a = 0, double b = 0) : x(a), y(b) {} friend bool operator < (const Point &l, const Point &r) { return l.y < r.y || (l.y == r.y && l.x < r.x); } } p[MAXN], ch[MAXN]; // p, point ch, convex hull double mult(Point a, Point b, Point o) { return (a.x - o.x) * (b.y - o.y) >= (b.x - o.x) * (a.y - o.y); } int Graham(Point p[], int n, Point res[]) { int top = 1; sort(p, p + n); if (n == 0) return 0; res[0] = p[0]; if (n == 1) return 0; res[1] = p[1]; if (n == 2) return 0; res[2] = p[2]; for (int i = 2; i < n; i++) { while (top && (mult(p[i], res[top], res[top - 1]))) top--; res[++top] = p[i]; } int len = top; res[++top] = p[n - 2]; for (int i = n - 3; i >= 0; i--) { while (top != len && (mult(p[i], res[top], res[top - 1]))) top--; res[++top] = p[i]; } return top; } int n; int main() { while (scanf("%d%d", &p .x, &p .y) != EOF) n++; n = Graham(p, n, ch); int t; for (int i = 0; i < n; i++) if (ch[i].x == 0 && ch[i].y == 0) { t = i; break; } for (int i = t; i < n; i++) printf("(%d,%d)\n", ch[i].x, ch[i].y); for (int i = 0; i < t; i++) printf("(%d,%d)\n", ch[i].x, ch[i].y); return 0; }
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