Codeforces Gym 100463D Evil DFS

题目链接:

http://codeforces.com/gym/100463

题意:

给你一个坐标系，上面有n个点，要求找到一个矩形，使得能够框住一半的红点，不框进任何一个蓝点，求最小矩形面积

题解:

暴力枚举，注意，矩形面积可以为0

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define MS(a) memset(a,0,sizeof(a))
#define MP make_pair
#define PB push_back
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
//////////////////////////////////////////////////////////////////////////
const int maxn = 1e5+10;

int n,num1,num2,ans;
struct node{
    int x,y;
}a[25],b[25];

bool check(int xl,int xr,int yl,int yr){
    for(int i=1; i<=num2; i++){
        if((b[i].x>=xl&&b[i].x<=xr) && (b[i].y>=yl&&b[i].y<=yr))
            return false;
    }
    return true;
}

void dfs(int u, int pre, int xmin,int xmax,int ymin,int ymax){
    if(u >= (num1)/2+1){
        if(check(xmin,xmax,ymin,ymax))
            ans = min(ans,(xmax-xmin)*(ymax-ymin));
        return ;
    }

    for(int i=pre+1; i<=num1; i++){
        dfs(u+1, i, min(xmin,a[i].x),max(xmax,a[i].x),min(ymin,a[i].y),max(ymax,a[i].y)); // 前驱等于后继的时候 考虑只有一个点的情况 也就是矩形面积为零
    }
}

int main(){
    int cas = 0;
    while(scanf("%d",&n),n){
        num1=num2=0;
        cas++;
        ans = INF;
        for(int i=1; i<=n; i++){
            int x=read(),y=read(),c=read();
            if(c == 0)
                a[++num1].x=x,a[num1].y=y;
            else
                b[++num2].x=x,b[num2].y=y;
        }

        dfs(1,0,INF,-INF,INF,-INF);
        if(ans != INF)
            cout << "Case " << cas << ": " << ans << endl;
        else
            cout << "Case " << cas << ": " << -1 << endl;
    }

    return 0;
}