Polygon core template

Xie Yong drew a picture and then solved the problem...

It is essentially a problem of "semi-plane interaction.

Straight cut polygon. The common part is the polygon core.

Here we find a good template:
Http://blog.csdn.net/accry/article/details/6070621

Http://blog.csdn.net/candy20094369/article/details/6703940

 

 

# Include <iostream> # include <cstdio> # include <cmath> # include <vector> # include <cstring> # include <algorithm> # include <string> # include <set> # include <ctime> # define Cl (ARR, val) memset (ARR, Val, sizeof (ARR) # define rep (I, n) for (I) = 0; (I) <(N ); ++ (I) # define for (I, L, H) for (I) = (l); (I) <= (h ); ++ (I) # define Ford (I, H, L) for (I) = (h); (I)> = (l); -- (I )) # define L (x) <1 # define R (x) <1 | 1 # define mid (L, R) (L + r)> 1 # define min (x, y) x <Y? X: y # define max (x, y) x <Y? Y: X # define e (x) (1 <(x) const double EPS = 1e-8; typedef long ll; using namespace STD; const int maxn = 110; struct point {Double X; Double Y; point (double A = 0, double B = 0): X (A), y (B) {} void input () {scanf ("% lf", & X, & Y) ;}; point [maxn], p [maxn], Q [maxn]; // The vertex (clockwise) of the read polygon, p is the array of the polygon vertices that are finally cut, and the vertex int ccnt, N of the saved core; // at this time, ccnt is the number of vertices for the final cut polygon and the number of saved vertices. inline int dbcmp (Double X) {// If (x> EPS) return 1; else if (x <-EPS) Return-1; return 0;} inline void Getline (point X, point y, double & A, double & B, double & C) {// point X, Y determines a straight line A = y. y-X. y; B = x. x-y. x; C = y. x * X. y-X. x * Y. y;} inline point intersect (point X, point y, double A, double B, double C) {// calculate the intersection of A, B, C, and a straight line formed by X and Y. double U = FABS (A * X. X + B * X. Y + C); Double V = FABS (A * Y. X + B * Y. Y + C); Return Point (X. x * V + Y. x * u)/(U + V), (X. y * V + Y. y * u)/(U + V);} inline void cut (double A, double B, double C) {// As shown in, cut int cur = 0, I; for (I = 1; I <= ccnt; ++ I) {If (dbcmp (A * P [I]. X + B * P [I]. Y + C)> = 0) Q [++ cur] = P [I]; // C may be too small due to precision problems, so some points should have been on the right, not on else {If (dbcmp (A * P [I-1]. X + B * P [I-1]. Y + C)> 0) // If P [I-1] is on the right of the line, // P [I], the intersection of a straight line formed by P [I-1] with a known straight line acts as a vertex of the core (in this way, the area of the core may be reduced due to precision issues) Q [++ cur] = intersect (P [I], p [I-1], a, B, c); If (dbcmp (A * P [I + 1]. X + B * P [I + 1]. Y + C)> 0) Q [++ cur] = intersect (P [I], p [I + 1], a, B, c );}} for (I = 1; I <= cur; ++ I) P [I] = Q [I]; P [cur + 1] = Q [1]; P [0] = P [cur]; ccnt = cur;} void solve () {// note: the default point is clockwise. if the subject is not clockwise, the normalization direction is int I; for (I = 1; I <= N; ++ I) {double A, B, C; Getline (point [I], point [I + 1],, b, c); cut (A, B, C);} If (ccnt = 0) puts ("no"); else puts ("yes ");} void Init () {int I; for (I, 1, n) point [I]. input (); point [n + 1] = point [1]; // initialize P [], ccnt for (I, 1, n) P [I] = point [I]; P [n + 1] = P [1]; P [0] = P [N]; ccnt = N ;} int main () {// freopen ("data. in "," r ", stdin); int t; scanf (" % d ", & T); While (t --) {scanf (" % d ", & N); Init (); solve ();} return 0 ;}