UVALive 6859 （凸包）

来源：互联网发布：wine for mac下载编辑：程序博客网时间：2024/06/06 04:48

将每个点分成上下左右四个点加入图中，求出凸包，由于只有长度为sqrt(2.0)和1的边，所以按照横坐标差值和纵坐标差值处理即可，代码如下：

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>#include <cmath>#include <queue>#include <map>#include <vector>using namespace std;typedef long long LL;const int maxn = 400007;double EPS = 1e-10;double add(double a, double b) {    if(abs(a+b) < EPS * (abs(a)+abs(b))) return 0;    return a+b;}struct P {    double x, y;    P() {}    P(double x, double y) : x(x), y(y) {}    P operator + (P p) { return P(add(x, p.x), add(y, p.y)); }    P operator - (P p) { return P(add(x,-p.x), add(y,-p.y)); }    P operator * (double d) { return P(x*d, y*d); }    double dot(P p) { return add(x*p.x, y*p.y); }    double det(P p) { return add(x*p.y, -y*p.x); }};bool cmp_x(const P& p, const P& q) {    if(p.x != q.x) return p.x < q.x;    return p.y < q.y;}vector<P> convex_hull(P* ps, int n) {    sort(ps, ps+n, cmp_x);    int k = 0;    vector<P> qs(n*2);    for(int i = 0; i < n; ++i) {        while(k > 1 && (qs[k-1]- qs[k-2]).det(ps[i] - qs[k-1]) <= 0 ) k--;        qs[k++] = ps[i];    }    for(int i = n-2, t = k; i >= 0; --i) {        while(k > t && (qs[k-1] - qs[k-2]).det(ps[i]-qs[k-1]) <= 0) k--;        qs[k++] = ps[i];    }    qs.resize(k-1);    return qs;}double dist(P p, P q) {    return (p-q).dot(p-q);}int N;P ps[maxn];void solve(int n) {    vector<P> qs = convex_hull(ps, n);    double res = 0.0;    int kk = qs.size();    double two = sqrt(2.0);    for(int i = 0; i < kk; ++i) {        int t1 = abs(qs[i].x-qs[(i-1+kk)%kk].x), t2 = abs(qs[i].y-qs[(i-1+kk)%kk].y);        res += abs(t1-t2);        res += (double)1.0*min(t1, t2)*two;    }    printf("%.5lf\n", res);}int main() {    int n;    while(~scanf("%d", &n)) {        int cnt = 0;        for(int i = 0; i < n; ++i) {            double x, y; scanf("%lf%lf", &x, &y);            ps[cnt].x = x+1;            ps[cnt++].y = y;            ps[cnt].x = x;            ps[cnt++].y = y+1;            ps[cnt].x = x-1;            ps[cnt++].y = y;            ps[cnt].x = x;            ps[cnt++].y = y-1;        }        solve(cnt);    }}

0 0