Wall(hdu 1348)

套用凸包的模板

要注意调用求叉积的函数multi时 所传参数的顺序……在这死了好一会……

#include <stdio.h>#include <algorithm>#include <math.h>#define pi atan(1.0) * 4using namespace std;struct point{int x, y;}p[1100], stack[1100];int top;double dis(point a, point b)  {//计算两点之间距离       return (sqrt(1.0 * ((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y))));  }  int multi(point a, point b, point c){return ((b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x));}int cmp(point a, point b){int m = multi(a, b, p[0]);if(m > 0)return 1;if(m == 0 && dis(a, p[0]) < dis(b, p[0]))return 1;//return 0;}void input(int n){int k = 0;for(int i = 0; i < n; i++){scanf("%d %d", &p[i].x, &p[i].y);if(p[i].x < p[k].x || (p[i].x == p[k].x && p[i].y < p[k].y))k = i;}point temp = p[k];p[k] = p[0];p[0] = temp;sort(p + 1, p + n, cmp);}void graham(int n){stack[0] = p[0];stack[1] = p[1];stack[2] = p[2];top = 2;for(int i = 3; i < n; i++){while(top > 0 && multi(stack[top - 1], p[i], stack[top]) > 0)top --;stack[++top] = p[i];} }int main (void){int t;scanf("%d", &t);while(t --){int n, l;scanf("%d %d", &n, &l);input(n);graham(n);double sum = 0;for(int i = 0; i < top; i++)sum += dis(stack[i], stack[i + 1]);sum += dis(stack[top], stack[0]);sum += 2 * pi * l;printf("%.lf\n", sum);if(t)printf("\n");}return 0;}