首页 > 代码库 > POJ 1265 计算几何 多边形面积 内部格点数 边上格点数
POJ 1265 计算几何 多边形面积 内部格点数 边上格点数
链接:
http://poj.org/problem?id=1265
题意:
给你一个多边形,求它的面积,内部格点数目,边上格点数目
题解:
pick公式:
给定顶点坐标均是整数点的简单多边形,有
面积=内部格点数目+边上格点数目/2+1
边界上的格点数:
把每条边当做左开右闭的区间以避免重复,一条左开右闭的线段(x1,y1)->(x2,y2)上的格点数为:
gcd(x2-x1,y2-y1)。
代码:
1 #include <map> 2 #include <set> 3 #include <cmath> 4 #include <queue> 5 #include <stack> 6 #include <cstdio> 7 #include <string> 8 #include <vector> 9 #include <cstdlib> 10 #include <cstring> 11 #include <sstream> 12 #include <iostream> 13 #include <algorithm> 14 #include <functional> 15 using namespace std; 16 #define rep(i,a,n) for (int i=a;i<n;i++) 17 #define per(i,a,n) for (int i=n-1;i>=a;i--) 18 #define all(x) (x).begin(),(x).end() 19 #define pb push_back 20 #define mp make_pair 21 #define lson l,m,rt<<1 22 #define rson m+1,r,rt<<1|1 23 typedef long long ll; 24 typedef vector<int> VI; 25 typedef pair<int, int> PII; 26 const ll MOD = 1e9 + 7; 27 const int INF = 0x3f3f3f3f; 28 const int MAXN = 2e4 + 7; 29 // head 30 31 const double eps = 1e-8; 32 int cmp(double x) { 33 if (fabs(x) < eps) return 0; 34 if (x > 0) return 1; 35 return -1; 36 } 37 38 const double pi = acos(-1); 39 inline double sqr(double x) { 40 return x*x; 41 } 42 struct point { 43 double x, y; 44 point() {} 45 point(double a, double b) :x(a), y(b) {} 46 void input() { 47 scanf("%lf%lf", &x, &y); 48 } 49 friend point operator+(const point &a, const point &b) { 50 return point(a.x + b.x, a.y + b.y); 51 } 52 friend point operator-(const point &a, const point &b) { 53 return point(a.x - b.x, a.y - b.y); 54 } 55 friend point operator*(const double &a, const point &b) { 56 return point(a*b.x, a*b.y); 57 } 58 friend point operator/(const point &a, const double &b) { 59 return point(a.x / b, a.y / b); 60 } 61 double norm() { 62 return sqrt(sqr(x) + sqr(y)); 63 } 64 }; 65 double det(point a, point b) { 66 return a.x*b.y - a.y*b.x; 67 } 68 double dot(point a, point b) { 69 return a.x*b.x + a.y*b.y; 70 } 71 double dist(point a, point b) { 72 return (a - b).norm(); 73 } 74 75 struct line { 76 point a, b; 77 line() {} 78 line(point x, point y) :a(x), b(y) {} 79 }; 80 double dis_point_segment(point p, point s, point t) { 81 if (cmp(dot(p - s, t - s)) < 0) return (p - s).norm(); 82 if (cmp(dot(p - t, s - t)) < 0) return (p - t).norm(); 83 return fabs(det(s - p, t - p) / dist(s, t)); 84 } 85 bool point_on_segment(point p, point s, point t) { 86 return cmp(det(p - s, t - s)) == 0 && cmp(dot(p - s, p - t)) <= 0; 87 } 88 bool parallel(line a, line b) { 89 return !cmp(det(a.a - a.b, b.a - b.b)); 90 } 91 bool line_make_point(line a, line b,point &res) { 92 if (parallel(a, b)) return false; 93 double s1 = det(a.a - b.a, b.b - b.a); 94 double s2 = det(a.b - b.a, b.b - b.a); 95 res = (s1*a.b - s2*a.a) / (s1 - s2); 96 return true; 97 } 98 99 struct polygon { 100 int n; 101 point a[MAXN]; 102 double area() { 103 double sum = 0; 104 a[n] = a[0]; 105 rep(i, 0, n) sum += det(a[i], a[i + 1]); 106 return sum / 2; 107 } 108 point MassCenter() { 109 point ans = point(0, 0); 110 if (cmp(area()) == 0) return ans; 111 a[n] = a[0]; 112 rep(i, 0, n) ans = ans + det(a[i + 1], a[i])*(a[i] + a[i + 1]); 113 return ans / area() / 6; 114 } 115 int gcd(int a, int b) { 116 return b == 0 ? a : gcd(b, a%b); 117 } 118 int Border_Int_Point_Num() { 119 int num = 0; 120 a[n] = a[0]; 121 rep(i, 0, n) num += gcd(abs(int(a[i + 1].x - a[i].x)), 122 abs(int(a[i + 1].y - a[i].y))); 123 return num; 124 } 125 int Inside_Int_Point_Num() { 126 return int(area()) + 1 - Border_Int_Point_Num() / 2; 127 } 128 }; 129 130 int n; 131 polygon p; 132 133 int main() { 134 int T; 135 cin >> T; 136 rep(cas, 1, T + 1) { 137 cin >> n; 138 p.n = n; 139 rep(i, 0, n) scanf("%lf%lf", &p.a[i].x, &p.a[i].y); 140 rep(i, 1, n) p.a[i] = p.a[i] + p.a[i - 1]; 141 int a = p.Inside_Int_Point_Num(); 142 int b = p.Border_Int_Point_Num(); 143 double c = p.area(); 144 printf("Scenario #%d:\n%d %d %.1f\n\n", cas, a, b, c); 145 } 146 return 0; 147 }
POJ 1265 计算几何 多边形面积 内部格点数 边上格点数
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