首页 > 代码库 > POJ3525 Most Distant Point from the Sea(半平面交)
POJ3525 Most Distant Point from the Sea(半平面交)
今天打算做两道半平面交,一题卡太久了,心都碎了。。。
?
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 | #pragma warning(disable:4996) #include <iostream> #include <cstring> #include <cstdio> #include <vector> #include <cmath> #include <string> #include <algorithm> using namespace std; #define maxn 2500 #define eps 1e-7 int n; int dcmp( double x){ return (x > eps) - (x < -eps); } struct Point { double x, y; Point(){} Point( double _x, double _y) :x(_x), y(_y){} Point operator + ( const Point &b) const { return Point(x + b.x, y + b.y); } Point operator - ( const Point &b) const { return Point(x - b.x, y - b.y); } Point operator *( double d) const { return Point(x*d, y*d); } Point operator /( double d) const { return Point(x / d, y / d); } double det( const Point &b) const { return x*b.y - y*b.x; } double dot( const Point &b) const { return x*b.x + y*b.y; } Point rot90(){ return Point(-y, x); } Point norm(){ double len= sqrt ( this ->dot(* this )); return Point(x, y) / len; } void read(){ scanf ( "%lf%lf" , &x, &y); } }; #define cross(p1,p2,p3) ((p2.x-p1.x)*(p3.y-p1.y)-(p3.x-p1.x)*(p2.y-p1.y)) #define crossOp(p1,p2,p3) (dcmp(cross(p1,p2,p3))) Point isSS(Point p1, Point p2, Point q1, Point q2){ double a1 = cross(q1, q2, p1), a2 = -cross(q1, q2, p2); return (p1*a2 + p2*a1) / (a1 + a2); } struct Border { Point p1, p2; double alpha; void setAlpha(){ alpha = atan2 (p2.y - p1.y, p2.x - p1.x); } }; bool operator < ( const Border &a, const Border &b) { int c = dcmp(a.alpha - b.alpha); if (c != 0) { return c == 1; } else { return crossOp(b.p1, b.p2, a.p1) > 0; } } bool operator == ( const Border &a, const Border &b){ return dcmp(a.alpha - b.alpha) == 0; } Point isBorder( const Border &a, const Border &b){ return isSS(a.p1, a.p2, b.p1, b.p2); } Border border[maxn]; Border que[maxn]; int qh, qt; // check函数判断的是新加的半平面和由a,b两个半平面产生的交点的方向,若在半平面的左侧返回True bool check( const Border &a, const Border &b, const Border &me){ Point is = isBorder(a, b); return crossOp(me.p1, me.p2, is) > 0; } bool convexIntersection() { qh = qt = 0; sort(border, border + n); n = unique(border, border + n) - border; for ( int i = 0; i < n; i++){ Border cur = border[i]; while (qh + 1 < qt&&!check(que[qt - 2], que[qt - 1], cur)) --qt; while (qh + 1 < qt&&!check(que[qh], que[qh + 1], cur)) ++qh; que[qt++] = cur; } while (qh + 1 < qt&&!check(que[qt - 2], que[qt - 1], que[qh])) --qt; while (qh + 1 < qt&&!check(que[qh], que[qh + 1], que[qt - 1])) ++qh; return qt - qh > 2; } Point ps[maxn]; bool judge( double x) { for ( int i = 0; i < n; i++){ border[i].p1 = ps[i]; border[i].p2 = ps[(i + 1) % n]; } for ( int i = 0; i < n; i++){ Point vec = border[i].p2 - border[i].p1; vec=vec.rot90().norm(); vec = vec*x; border[i].p1 = border[i].p1 + vec; border[i].p2 = border[i].p2 + vec; border[i].setAlpha(); } return convexIntersection(); } int main() { while (cin>>n&&n) { for ( int i = 0; i < n; i++){ ps[i].read(); } double l=0, r=100000000; while (dcmp(r-l)>0){ double mid = (l + r) / 2; if (judge(mid)) l = mid; else r = mid; } printf ( "%.6lf\n" , l); } return 0; } |
声明:以上内容来自用户投稿及互联网公开渠道收集整理发布,本网站不拥有所有权,未作人工编辑处理,也不承担相关法律责任,若内容有误或涉及侵权可进行投诉: 投诉/举报 工作人员会在5个工作日内联系你,一经查实,本站将立刻删除涉嫌侵权内容。