hdu 1348(凸包)

/*
*  凸包
*  注意：给出的点为整点数，不要设某一精度值！ 
*/

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>

using namespace std;

const int N = 1005;
const double PI = 3.1415927;

struct point {
    double x;
    double y;
}p[N], stack[N];

double dis(point A, point B) {
    return sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
}

double crossProd(point A, point B, point C) {
    return (B.x-A.x)*(C.y-A.y) - (B.y-A.y)*(C.x-A.x);
}

//以最左下的点为基准点，其他各点（逆时针方向）以极角从小到大的排序规则
int cmp(const void *a, const void *b) {
    point *c = (point *)a;
    point *d = (point *)b;
    double k = crossProd(p[0], *c, *d);//极角大小转化为求叉乘
    if (k<0 || !k && dis(p[0], *c)>dis(p[0], *d)) return 1;
    return -1;
}

double Graham(int n) {
    double x = p[0].x;
    double y = p[0].y;
    int mi = 0;
    for (int i=1; i<n; ++i) {//找到最左下的一个点
        if (p[i].x<x || (p[i].x==x && p[i].y<y)) {
            x = p[i].x;
            y = p[i].y;
            mi = i;
        }
    }
    point tmp = p[mi];
    p[mi] = p[0];
    p[0] = tmp;
    qsort(p+1, n-1, sizeof(point), cmp);
    p[n] = p[0];
    stack[0] = p[0];
    stack[1] = p[1];
    stack[2] = p[2];
    int top = 2;
    for (int i=3; i<=n; ++i) {//加入一个点后,向右偏拐或共线，则上一个点不在凸包内，则--top，该过程直到不向右偏拐或没有三点共线的点 
        while (crossProd(stack[top-1], stack[top], p[i])<=0 && top>=2) --top;
        stack[++top] = p[i];//在当前情况下符合凸包的点，入栈
    }
    double len = 0;
    for (int i=0; i<top; ++i) len += dis(stack[i], stack[i+1]);
    return len;
}

int main() {
    int t;
    while (scanf("%d", &t) != EOF) {
        while (t--) {
            int n, l;
            scanf ("%d%d", &n, &l);
            for (int i=0; i<n; ++i) scanf ("%lf%lf", &p[i].x, &p[i].y);
            double ans = Graham(n);
            ans += PI * (l + l);
            printf ("%.0lf\n", ans);
            if (t) printf ("\n");
        }
    }
    return 0;
}