HDU 4946 area of mushroom (coaxial convex hull)

HDU 4946 area of mushroom

Question Link

Some people have a speed in one location. If a person is faster than anyone else, the person is in charge of that location, the number of people in a region is infinite.

Train of Thought: Just take out the persons with the highest speed for consideration. Then, if you want to find a wildcard convex bag, the persons with the convex bag will be infinitely large. Pay attention to special common points, note that none of the above is infinite, and pay attention to the case of 0.

Code:

#include<cstdio>#include <cstring>#include<cmath>#include<algorithm>#include <map>#include<iostream>using namespace std;const int N = 505;struct point {    int x,y,val,id;} list[N], save[N], p[N];int stack[N],top, vi[N];int cross(point p0,point p1,point p2) {    return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);}    double dis(point p1,point p2) {    return sqrt((double)(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y));}bool cmp(point p1,point p2) {    int tmp=cross(list[0],p1,p2);    if(tmp>0) return true;    else if(tmp==0&&dis(list[0],p1)<dis(list[0],p2)) return true;    else return false;}void init(int n) {    int i,k;    point p0;    list[0] = p[0];    p0.x=list[0].x;    p0.y=list[0].y;    p0.id = list[0].id;    k=0;    for(i=1;i<n;i++) {list[i] = p[i];if( (p0.y>list[i].y) || ((p0.y==list[i].y)&&(p0.x>list[i].x)) ) {    p0.x=list[i].x;    p0.y=list[i].y;    p0.id = list[i].id;    k=i;}        }        list[k]=list[0];    list[0]=p0;    sort(list+1,list+n,cmp);}     void graham(int n) {    int i;    if(n==1) {top=0;stack[0]=0;}    if(n==2) {top=1;stack[0]=0;stack[1]=1;    }        if(n>2) {for(i=0;i<=1;i++) stack[i]=i;top=1;for(i=2;i<n;i++) {    while(top>0&&cross(list[stack[top-1]],list[stack[top]],list[i])<0) top--;    top++;    stack[top]=i;}memset(vi, 0, sizeof(vi));for (int i = 0; i <= top; i++)    vi[stack[i]] = 1;int tmp = top;for (int i = n - 1; i >= 0; i--) {    if (i == stack[0] || i == stack[top]) continue;    if (!vi[i] && cross(list[stack[0]], list[stack[top]], list[i]) == 0)stack[++tmp] = i;}top = tmp;    }    }int n, pn, vis[N];map<pair<int, int>, int> sb;void solve() {    for (int i = 0; i <= top; i++)vis[list[stack[i]].id] = 1;    for (int i = 0; i < pn; i++) {if (sb[make_pair(p[i].x, p[i].y)] > 1)    vis[p[i].id] = 0;    }}int main() {    int cas = 0;    while (~scanf("%d", &n) && n) {printf("Case #%d: ", ++cas);sb.clear();memset(vis, 0, sizeof(vis));int Max = 0;for (int i = 0; i < n; i++) {    scanf("%d%d%d", &save[i].x, &save[i].y, &save[i].val);    save[i].id = i;    Max = max(Max, save[i].val);}if (Max == 0) {    for (int i = 0; i < n; i++)printf("0");    printf("\n");    continue;}pn = 0;for (int i = 0; i < n; i++) {    if (save[i].val == Max) {if (!sb.count(make_pair(save[i].x, save[i].y))) {    p[pn++] = save[i];    sb[make_pair(save[i].x, save[i].y)] = 1;    continue;}sb[make_pair(save[i].x, save[i].y)]++;    }}if (pn) {    init(pn);    graham(pn);    solve();}for (int i = 0; i < n; i++)    printf("%d", vis[i]);printf("\n");    }    return 0;}