Poj 1279 art gallery-calculate the area of the polygon Core

/* Poj 1279 art gallery-calculate the area of the polygon core */# include <stdio. h> # include <math. h ># include <algorithm> using namespace STD; const double EPS = 1e-8; struct point {Double X, Y;} Dian [20000 + 10]; point Jiao [203]; struct line {point S, E; double angle;} Xian [20000 + 10]; int N, Yong; bool mo_ee (Double X, Double Y) {double ret = x-y; If (Ret <0) ret =-ret; If (Ret <EPS) return 1; return 0;} bool mo_gg (Double X, double Y) {return x> Y + EPS;} // x> Y bool mo_ll (Double X, Double Y) {return x <Y-EPS ;} // x <y bool mo_ge (Double X, Double Y) {return x> Y-EPS;} // x> = y bool mo_le (Double X, Double Y) {return x <Y + EPS;} // x <= y point mo_intersection (point u1, point U2, point V1, point V2) {point ret = U1; double T = (u1.x-v1.x) * (v1.y-v2.y)-(u1.y-v1.y) * (v1.x-v2.x)/(u1.x-u2.x) * (v1.y-v2.y)-(u1.y-u2.y) * (v1.x-v2.x); ret. X + = (u2.x-u1.x) * t; ret. Y + = (u2.y-u1.y) * t; return ret;} double mo_xmult (point P2, point P0, Point P1) // P1 returns a negative value on the left of P2, return positive {return (p1.x-p0.x) * (p2.y-p0.y)-(p2.x-p0.x) * (p1.y-p0.y);} void mo_hpi_addl (point a, point B) on the right) {Xian [Yong]. S = A; Xian [Yong]. E = B; Xian [Yong]. angle = atan2 (B. y-a.y, B. x-a.x); Yong ++;} // half plane bool mo_hpi_cmp (const line & A, const line & B) {If (mo_ee (. angle, B. angle) {return mo_gg (mo_xmult (B. e,. s, B. s), 0);} else {return mo_ll (. angle, B. angle) ;}} int mo_hpi_dq [20000 + 10]; bool mo_hpi_isout (line cur, line Top, line top_1) {point Jiao = mo_intersection (top. s, top. e, top_1.s, top_1.e); Return mo_ll (mo_xmult (cur. e, Jiao, cur. s), 0);} int mo_halfplaneintersect (line * Xian, int N, point * Jiao) {int I, j, ret = 0; sort (Xian, Xian + N, mo_hpi_cmp); for (I = 0, j = 0; I <n; I ++) {If (mo_gg (xian [I]. angle, Xian [J]. angle) {Xian [++ J] = Xian [I] ;}} n = J + 1; mo_hpi_dq [0] = 0; mo_hpi_dq [1] = 1; int Top = 1, bot = 0; for (I = 2; I <n; I ++) {While (top> bot & mo_hpi_isout (xian [I], xian [mo_hpi_dq [Top], Xian [mo_hpi_dq [Top-1]) Top --; while (top> bot & mo_hpi_isout (xian [I], xian [mo_hpi_dq [bot], Xian [mo_hpi_dq [bot + 1]) BOT ++; mo_hpi_dq [++ top] = I; // current half-plane inbound stack} while (top> bot & mo_hpi_isout (xian [mo_hpi_dq [bot], Xian [mo_hpi_dq [Top], xian [mo_hpi_dq [Top-1]) Top --; while (top> bot & mo_hpi_isout (xian [mo_hpi_dq [Top], Xian [mo_hpi_dq [bot], xian [mo_hpi_dq [bot + 1]) BOT ++; mo_hpi_dq [++ top] = mo_hpi_dq [bot]; for (ret = 0, I = Bot; I <top; I ++, RET ++) {Jiao [RET] = mo_intersection (xian [mo_hpi_dq [I + 1]. s, Xian [mo_hpi_dq [I + 1]. e, Xian [mo_hpi_dq [I]. s, Xian [mo_hpi_dq [I]. e);} return ret;} // calculate the Polygon Area Double mo_area_polygon (point * Dian, int N) {int I; point yuan; yuan. X = yuan. y = 0; double ret = 0; for (I = 0; I <n; ++ I) {RET + = mo_xmult (Dian [(I + 1) % N], yuan, Dian [I]);} return ret;} int main () {int I, iofcase = 1, t; scanf ("% d", & T ); while (t --) {scanf ("% d", & N); Yong = 0; for (I = 0; I <n; ++ I) {scanf ("% lf", & Dian [I]. x, & Dian [I]. y);} double area = mo_area_polygon (Dian, n); If (area <0) // if it is clockwise {for (I = 0; I <n; ++ I) {mo_hpi_addl (Dian [(I + 1) % N], Dian [I]) ;}} else {for (I = 0; I <n; ++ I) {mo_hpi_addl (Dian [I], Dian [(I + 1) % N]) ;}} int ret = mo_halfplaneintersect (Xian, N, Jiao); Area = mo_area_polygon (Jiao, RET); If (area <0) Area =-area; Area = Area/2; printf ("%. 2lf \ n ", area);} return 0 ;}