Poj 3850 simple polygon

/* Question: given some vertices, find a sequence of points and follow the sequence connection point (the beginning and end are also connected) to form a polygon (any line and other lines do not want to be handed in) just sort the polar angles directly. Pay attention to the case of Collinearity, except for the first place with a very small distance from the starting position, other locations are far away from the pole */# include <cstdio> # include <cstring> # include <cmath> # include <cstdlib> const int maxn = 2009; const double EPS = 1e-8; struct point {Double X, Y; int ID;} p [maxn], H [maxn]; inline double distance (const point & P1, const point & p2) {return SQRT (p1.x-p2.x) * (p1.x-p2.x) + (p1.y-p2.y) * (p1.y-p2.y ));} // calculate the inline double multiply (const point & sp, const point & EP, const point & OP) {return (sp. x-op.x) * (Ep. y-op.y)-(Ep. x-op.x) * (sp. y-op.y);} // determine whether SP, EP, OP meet the left turn int CMP (const void * a, const void * B) {// sort point * P1 = (point *) A; point * P2 = (point *) B; Double T = multiply (* P2, * P1, P [0]); If (T> EPS) return 1; else if (FABS (t) <= EPS) {If (distance (P [0], * P1) <distance (P [0], * P2) return 1; else return-1;} else return-1;} int CMP1 (const void * a, const void * B) {// sort point * P1 = (point *) A; point * P2 = (point *) B; Double T = multiply (* P2, * P1, P [0]); If (T> EPS) return 1; else if (FABS (t) <= EPS) {If (distance (P [0], * P1)> distance (P [0], * P2) return 1; else return-1;} else return-1;} void anglesort (point P [], int N) {// find the point int I, K = 0; point temp; for (I = 1; I <n; I ++) if (P [I]. x <p [K]. X | (P [I]. X = P [K]. x) & (P [I]. Y <p [K]. y) k = I; temp = P [0], p [0] = P [K], p [k] = temp; qsort (p + 1, n-1, sizeof (point), CMP); for (I = 2; I <n; I ++) // find the vertices on the edge, re-order if (FABS (multiply (P [0], p [1], p [I])> EPS) {break;} qsort (p + 1, I-1, sizeof (point), CMP1);} void graham_scan (point P [], point ch [], int N, Int & Len) {// create a convex packet int I, top = 2; anglesort (p, n);} int main () {int I, j, N, Len; double D, ans; int CA; scanf ("% d", & Ca); While (ca --) {scanf ("% d", & N); for (I = 0; I <N; I ++) {scanf ("% lf", & P [I]. x, & P [I]. y); P [I]. id = I;} graham_scan (p, H, N, Len); int flag = 1; for (INT I = 0; I <n; I ++) {If (FLAG) {printf ("% d", P [I]. ID); flag = 0; continue;} printf ("% d", P [I]. ID);} puts ("");} return 0 ;}