PKU 1113 Wall .
Your task is to help poor Architect to save his head, by writing a program that will find the minimum possible length of the wall that he could build around the castle to satisfy King's requirements.
The task is somewhat simplified by the fact, that the King's castle has a polygonal shape and is situated on a flat ground. The Architect has already established a Cartesian coordinate system and has precisely measured the coordinates of all castle's vertices in feet.
#include <iostream>#include <vector>#include <cmath>#include <algorithm>using namespace std;#define MAXI 1011#define sq(x) ((x) * (x)) //Squarestruct pt { double x, y; } ps[MAXI];vector<pt> st; //Pseudo-Stack {= =}int n, len;double l;double dlt(pt &a, pt &b, pt &o) //Cross-Product{return (o.x - a.x) * (b.y - a.y) - (b.x - a.x) * (o.y - a.y);}double dis(pt &a, pt &b) //Distance{return sqrt(sq(a.x - b.x) + sq(a.y - b.y));}bool pac(pt &a, pt &b) //Polar-Angle-Compare{double delta = dlt(a, b, ps[0]);if ( delta == 0 && sq(a.x - ps[0].x) + sq(a.y - ps[0].y) > sq(b.x - ps[0].x) + sq(b.y - ps[0].y))return 1;else if (delta < 0)return 1;return 0;}void pas() //Polar-Angle-Sort{int i, id;for (id = 0, i = 1; i < n; i++)if ((ps[i].y == ps[id].y && ps[i].x < ps[id].x) || ps[i].y < ps[id].y)id = i;swap(ps[0], ps[id]);sort(ps + 1, ps + n, pac);#if 0for (i = 0; i < n; i++)printf("p%d = [%lf, %lf]\n", i, ps[i].x, ps[i].y);#endif}void ghs() //Graham's-Scan{int i;pas();len = 2;st.clear();st.push_back(ps[0]);st.push_back(ps[1]);for (i = 2; i < n; i++)if (dlt(st[1], ps[i], st[0]) != 0)break;st.push_back(ps[2]);for (i++; i < n; i++){while (dlt(st[len], ps[i], st[len - 1]) >= 0){st.pop_back();len--;}st.push_back(ps[i]);len++;}len++;#if 0for (i = 0; i < len; i++)printf("p%d = [%lf, %lf]\n", i, st[i].x, st[i].y);#endif}double sta() //Statistic{int i;double tsu = 0.0;for (i = 0; i < len; i++)tsu += dis(st[i % len], st[(i + 1) % len]);#if 0printf("%lf\n", dlt(st[1], st[2], st[0]) / (dis(st[0], st[1]) * dis(st[1], st[2])));#endifreturn tsu + 4.0 * asin(1.0) * l;}int main(){int i;#if 0printf("%lf\n", 4.0 * asin(1.0) * 100);#endifwhile (scanf("%d%lf", &n, &l) != EOF){for (i = 0; i < n; i++)scanf("%lf%lf", &ps[i].x, &ps[i].y);ghs();printf("%d\n", (int)(sta() + 0.5));}return 0;}
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第一次用代码控件…………
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