2019ccpc河北省赛 A Battle of Balls

行了这是个裸的判联通的题，dfs bfs 并查集均可

这是并查集的做法

#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const int maxn = 1e3 + 10;
int sgn(double x) {
    if (fabs(x) < eps) return 0;
    else return x > 0 ? 1 : -1;
}
int n;
double r;
double x[maxn], y[maxn];
int fa[maxn];
void Init() {for (int i = 0; i < maxn; ++i) fa[i] = i;} 
int find(int X) {return X == fa[X] ? fa[X] : fa[X] = find(fa[X]);}
void Unin(int X, int Y) {
    X = find(X);
    Y = find(Y);
    if (X != Y) {
        fa[X] = Y;
    }
} 
double dis(int i, int j) {
    return hypot(x[i] - x[j], y[i] - y[j]);
}
int main() {
    int t;
    scanf("%d", &t);
    while (t--) {
        Init();
        scanf("%d %lf", &n, &r);
        r *= 2.0;
        for (int i = 1; i <= n; ++i) {
            scanf("%lf %lf", x + i, y + i);
        }
        for (int i = 1; i <= n; ++i) {
            if (sgn(x[i] - r) <= 0) {
                Unin(0, i);
            }
            if (sgn(100 - x[i] - r) <= eps) {
                Unin(i, n + 1);
            }
        }
        for (int i = 1; i <= n; ++i) {
            for (int j = i + 1; j <= n; ++j) {
                if (sgn(dis(i, j) - r) <= 0) {
                    Unin(i, j);
                }
            }
        }
        puts(find(0) != find(n + 1) ? "Yes" : "No");
    }
    return 0;
}

dfs做法

#include <bits/stdc++.h>
#include<vector>
using namespace std;
typedef long long LL;
typedef pair<double, double> pdd;
const int N = 1e3 + 10;
const int M = 2e6 + 10;
const int inf = 0x3f3f3f3f;
const double eps = 1e-5;
 
double x[N];
double y[N];
vector<int> G[N];
bool vis[N];
 
bool dfs(int u) {
    vis[u]=true;
    if(!u) return true;
    vector<int>::iterator it;
    for(it=G[u].begin();it!=G[u].end();it++)
    	if(!vis[*it])
    		if(dfs(*it))return true;
			
    return false;
}
 
int main() {
    int T;cin>>T;
    for (;T--;) {
        int n;
        double r;
        scanf("%d%lf",&n,&r);
        for(int i=1;i<=n;i++)
            scanf("%lf%lf",&x[i],&y[i]);
        double d=2*r,d2=d*d;
        if (d >= 100) {
            puts("No");
            continue;
        }
        for (int i = 1; i <= n; i++) {
            if (x[i] <= d) {
                G[0].push_back(i);
                G[i].push_back(0);
            }
            if (100 - x[i] <= d) {
                G[n + 1].push_back(i);
                G[i].push_back(n + 1);
            }
        }
 
        for (int i = 1; i <= n; i++) {
            for (int j = i + 1; j <= n; j++) {
                double f = (x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]);
                if (f - d2 <= eps) {
                    G[i].push_back(j);
                    G[j].push_back(i);
                }
            }
        }
 
        if (dfs(n + 1)) puts("No");
        else puts("Yes");
        for (int i = 0; i <= n + 1; i++) {
            G[i].clear();
            vis[i] = false;
        }
    }
    return 0;
}

bfs 牛客网copy的己卯年三月十二 的代码

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include<bits/stdc++.h>
#include <stdlib.h>
using namespace std;
#define ull unsigned long long
#define ll long long
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef pair<double,int> pdi;
const int maxn=1e3+5;
const double eps=1e-8;
pdd a[maxn];
int n,vis[maxn];
double r;
vector<int> G[maxn];
bool touchL(int x){
    return a[x].first-2.0*r<eps;
}
bool touchR(int x){
    return 100.0-a[x].first-2.0*r<eps;
}
bool touch(int x,int y){
    double dx=a[x].first-a[y].first,dy=a[x].second-a[y].second;
    return dx*dx+dy*dy-4.0*r*r<eps;
}
bool bfs(void){
    if(100.0-2.0*r<eps) return false;
    queue<int> q;
    memset(vis,0,sizeof(vis));
    for(int i=1;i<=n;++i)if(touchL(i)) q.push(i),vis[i]=1;
    if(q.empty()) return true;
    while(!q.empty()){
            int u=q.front();q.pop();
            if(touchR(u)) return false;
            for(int i=0;i<G[u].size();++i)if(!vis[G[u][i]]){
                    int v=G[u][i];vis[v]=1;
                    q.push(v);
            }
    }
    return true;
}
int main(void){
    int T;scanf("%d",&T);
    while(T--){
            scanf("%d%lf",&n,&r);
            for(int i=1;i<=n;++i){
                    G[i].clear();
                    scanf("%lf%lf",&a[i].first,&a[i].second);
            }
            for(int i=1;i<=n;++i)
            for(int j=1;j<i;++j)if(touch(i,j)){
                    G[i].push_back(j);G[j].push_back(i);
            }
            if(bfs()) puts("Yes");
            else puts("No");
    }
    return 0;
}