HDU 1392 Surround the Trees .

Surround the Trees

Time Limit: 2000/1000 MS (Java/Others)????Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 3223????Accepted Submission(s): 1230

There are no more than 100 trees.
#include <iostream>#include <vector>#include <cmath>#include <cstdlib>#include <algorithm>using namespace std;#define MAXI 111class point{public : double x, y; point(double tx = 0.0, double ty = 0.0) { x = tx; y = ty; } double dis() { return sqrt(pow(x, 2) + pow(y, 2)); }; point operator - (point &o) { return point(x - o.x, y - o.y); } double operator * (point &o) { return x * o.y - y * o.x; }}ps[MAXI];vector<point> chul;int n;bool cmp(point &a, point &b){ double cp = (ps[0] - a) * (b - a); if (cp == 0) return (a - ps[0]).dis() > (b - ps[0]).dis(); else if (cp < 0) return 1; return 0;}double GHS(){ int i, idm; double tsu = 0.0; for (idm = i = 0; i < n; i++) if (ps[i].y == ps[idm].y && ps[i].x < ps[idm].x || ps[i].y < ps[idm].y) idm = i; swap(ps[idm], ps[0]); sort(ps + 1, ps + n, cmp); chul.clear(); chul.push_back(ps[0]); chul.push_back(ps[1]); for (i = 2; (ps[0] - ps[1]) * (ps[i] - ps[1]) == 0; i++); chul.push_back(ps[i]); for (i++; i < n; i++) { while ((chul[chul.size() - 2] - chul[chul.size() - 1]) * (ps[i] - chul[chul.size() - 1]) >= 0) chul.pop_back(); chul.push_back(ps[i]); } for (i = 0; i < chul.size(); i++) tsu += (chul[(i + 1) % chul.size()] - chul[i]).dis(); return tsu;}int main(){ int i; while (scanf("%d", &n), n) { for (i = 0; i < n; i++) scanf("%lf%lf", &ps[i].x, &ps[i].y); if (n == 2) printf("%.2lf\n", ps[1] - ps[0]); else if (n == 1) printf("0\n"); else printf("%.2lf\n", GHS()); } return 0;}

?Thanks……