【凸包】HDU 4946 Area of Mushroom

注意：

1.重合的点

2.速度为０的点

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <ctype.h>
#include <math.h>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
#include <queue>
#include <stack>
#include <vector>
typedef long long LL;
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define N 500005
#define maxn 505
struct Point
{
    int x, y;
    int id, v;
    bool flag;
    Point(int x = 0, int y = 0) : x(x), y(y) { }
} p[maxn], ch[maxn];
int ans[maxn], n;
Point operator - (Point a, Point b)
{
    return Point(a.x - b.x, a.y - b.y);
}
int Cross(Point a, Point b)
{
    return a.x * b.y - a.y * b.x ;
}
int cmp(Point a, Point b)
{
    if(a.x != b.x) return a.x < b.x;
    else if ( a.y != b.y ) return a.y < b.y;
    else return a.v>b.v;
}
int cmp1(Point a, Point b)
{
    return a.v > b.v;
}
int ConvexHull(Point* p, int n, Point* ch)
{
    sort(p, p+n, cmp);
    for(int i=0; i<n-1 ; i++)
        if(p[i].x==p[i+1].x && p[i].y==p[i+1].y && p[i].v==p[i+1].v)
            p[i].flag=1;
    int m = 0;
    for(int i=0; i<n; i++)
    {
        if(p[i].flag==1)
            continue;
        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--)
    {
        if(p[i].flag==1)
            continue;
        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 main()
{
    int ca=1;
    while(~scanf("%d", &n) && n)
    {
        memset(p, 0, sizeof(p));
        memset(ans, 0, sizeof(ans));
        memset(ch, 0, sizeof(ch));
        for(int i=1;i<=n;i++)
        {
            scanf("%d%d%d", &p[i].x, &p[i].y, &p[i].v);
            p[i].id=i;
        }
        printf("Case #%d: ", ca++);
        int i, m;
        sort(p+1, p+1+n, cmp1);
        if(p[1].v==0)
        {
            for(i=1; i<=n; i++)
                printf("0");
            printf("\n");
            continue;
        }
        for(i = 1; i < n; i++)
            if(p[i].v != p[i+1].v)
                break;
        m=ConvexHull(p+1, i, ch);
        for(i = 0; i < m; i++)
            ans[ch[i].id] = 1;
        sort (p+1, p+n+1, cmp);
        for(i=1; i<n; i++)
            if (p[i].x==p[i + 1].x && p[i].y==p[i + 1].y)
                if(p[i].v==p[i + 1].v)
                    ans[p[i].id] = ans[p[i + 1].id] = 0 ;
        for(i=1; i<=n; i++)
            printf("%d", ans[i]);
        printf("\n");
    }
    return 0;
}

【凸包】HDU 4946 Area of Mushroom