UVALive4728

来源：互联网发布：淘宝暗语编辑：程序博客网时间：2024/05/22 22:28

题目链接：https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2729

正方形的每个点都找出来，做凸包，距离最大的肯定都是凸包上的点，然后找対踵点对：先固定点u到u+1这条有向边，v到v+1的边从u到u+1的下一条边开始旋转，一直到两条边的叉积小于0，这个时候点 v 就是 u 的対踵点，如果叉积等于0 的话，v+1也是 u 的対踵点；找到u的対踵点之后就更新最大值，然后找u+1的対踵点。

（刘汝佳的模板）

#include <iostream>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;const double eps = 1e-10;struct Point{    int x, y;    Point() {}    Point(int x, int y):x(x), y(y) {}    bool operator < (const Point& a) const    {        if (x == a.x)            return y < a.y;        return x < a.x;    }    bool operator == (const Point& a) const    {        return x == a.x && y == a.y;    }};typedef Point Vector;Point P[400040], convex[400040];Vector operator - (Point A, Point B){    return Vector(A.x-B.x, A.y-B.y);}int Cross(Vector A, Vector B){    return A.x*B.y - A.y*B.x;}int ConvexHull(Point *p, int n, Point *ch){    sort(p, p+n);    n = unique(p, p+n) - p;    int m = 0;    for (int i=0; i<n; i++)    {        while (m > 1 && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;        ch[m++] = p[i];    }    int k = m;    for (int i=n-2; i>=0; i--)    {        while (m > k && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2]) <= 0) m--;        ch[m++] = p[i];    }    if (n > 1)        m--;    return m;}int dis(Point a, Point b){    return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);}int diameter(Point *convex, int n){    int ans = 0;    if (n == 1)            return 0;    if (n == 2)        return dis(convex[0],convex[1]);    for (int u=0, v=1; u<n; u++)    {        for (;;)        {            int k = Cross(convex[u+1]-convex[u], convex[v+1]-convex[v]);            if (k <= 0)            {                ans = max(ans, dis(convex[u],convex[v]));                if (k == 0)                    ans = max(ans, dis(convex[u],convex[v+1]));                break;            }            v = (v+1) % n;        }    }    return ans;}int main(){    int t;    scanf("%d",&t);    while (t > 0)    {        t--;        int n;        int cnt = 0;        scanf("%d",&n);        for (int i=0; i<n; i++)        {            int x, y, w;            scanf("%d%d%d",&x, &y, &w);            P[cnt++] = Point(x,y);            P[cnt++] = Point(x, y+w);            P[cnt++] = Point(x+w, y);            P[cnt++] = Point(x+w, y+w);        }        int m = ConvexHull(P,cnt,convex);        printf("%d\n",diameter(convex, m));    }    return 0;}

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