Bridge Across Islands POJ

Bridge Across Islands

POJ - 3608

题意：求凸包最近距离．

旋转卡壳～

转自：Gitfan

#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const int inf = 0x3f3f3f3f;
const int maxn = 10010;

struct Point{
    double x, y;
    Point(double x = 0, double y = 0): x(x), y(y){}
};
typedef Point Vector;

Vector operator - (Point a, Point b) {
    return Vector(a.x - b.x, a.y - b.y);
}
Vector operator + (Vector a, Vector b) {
    return Vector(a.x + b.x, a.y + b.y);
}
Vector operator * (Vector a, double p) {
    return Vector(a.x * p, a.y * p);
}
Vector operator / (Vector a, double p) {
    return Vector(a.x / p, a.y / p);
}
bool operator < (Point a, Point b) {
    return a.x < b.x || a.x == b.x && a.y < b.y;
}
int dcmp(double x) {
    if(fabs(x) < eps) return 0;
    return x < 0 ? -1 : 1;
}

bool operator == (Point a, Point b) {
    return dcmp(a.x - b.x) == 0 && dcmp(a.y - b.y) == 0;
}
double Dot(Vector a, Vector b) {
    return a.x * b.x + a.y * b.y;
}
double Cross(Vector a, Vector b) {
    return a.x * b.y - a.y * b.x;
}
double Length(Vector a) {
    return sqrt(Dot(a, a));
}
double Angle(Vector a) {
    return atan2(a.y, a.x);
}
double DistanceToSegment(Point p, Point a, Point b) {
    if(a == b) return Length(p-a);
    Vector v1 = b - a, v2 = p - a, v3 = p - b;
    if(dcmp(Dot(v1, v2)) < 0) return Length(v2);
    if(dcmp(Dot(v1, v3)) > 0) return Length(v3);
    return fabs(Cross(v1, v2)) / Length(v1);
}
double SegmentDistance(Point a1, Point b1, Point a2, Point b2) {
    return min(min(DistanceToSegment(a1, a2, b2), DistanceToSegment(b1, a2, b2)),
               min(DistanceToSegment(a2, a1, b1), DistanceToSegment(b2, a1, b1)));
}
//两凸包的最短距离
double RotateCalipers(Point *p1, int n, Point *p2, int m) {
    int minp1 = 0, maxp2 = 0;
    for(int i = 0; i < n; i++){
        if(p1[i].y < p1[minp1].y) minp1 = i;
    }
    for(int i = 0; i < m; i++){
        if(p2[i].y > p2[maxp2].y) maxp2 = i;
    }
    p1[n] = p1[0];
    p2[m] = p2[0];
    double dis = inf, temp;
    for(int i = 0; i < n; i++) {
        while(dcmp(Cross(p1[minp1] - p1[minp1+1], p2[maxp2+1] - p1[minp1+1]) - Cross(p1[minp1] - p1[minp1+1], p2[maxp2] - p1[minp1+1])) < 0) maxp2 = (maxp2+1) % m;
        dis = min(dis, SegmentDistance(p1[minp1], p1[minp1+1], p2[maxp2], p2[maxp2+1]));
        minp1 = (minp1+1) % n;
    }
    return dis;
}
Point p1[maxn], p2[maxn];
int main(){
    int n, m;
    //freopen("in.txt", "r", stdin);
    while(scanf("%d %d", &n, &m) && (n+m)) {
        for(int i = 0; i < n; i++){
            scanf("%lf %lf", &p1[i].x, &p1[i].y);
        }
        for(int i = 0; i < m; i++){
            scanf("%lf %lf", &p2[i].x, &p2[i].y);
        }
        printf("%lf
", RotateCalipers(p1, n, p2, m));
    }
    return 0;
}