HDU 3622 Bomb Game

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <cmath>
  5 #include <algorithm>
  6 #include <climits>
  7 #include <vector>
  8 #include <queue>
  9 #include <cstdlib>
 10 #include <string>
 11 #include <set>
 12 #include <stack>
 13 #define LL long long
 14 #define pii pair<int,int>
 15 #define INF 0x3f3f3f3f
 16 using namespace std;
 17 const int maxn = 250;
 18 const double exps = 1e-5;
 19 struct arc{
 20     int to,next;
 21     arc(int x = 0,int y = -1){
 22         to = x;
 23         next = y;
 24     }
 25 };
 26 struct node{
 27     int x,y;
 28 };
 29 node p[maxn];
 30 arc e[maxn*maxn*10];
 31 int head[maxn],tot,dfn[maxn],low[maxn],belong[maxn],scc,cnt,n;
 32 bool instack[maxn];
 33 stack<int>stk;
 34 void add(int u,int v){
 35     e[tot] = arc(v,head[u]);
 36     head[u] = tot++;
 37 }
 38 double dis(const node &a,const node &b){
 39     double tmp = (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y);
 40     return sqrt(tmp);
 41 }
 42 void tarjan(int u){
 43     dfn[u] = low[u] = ++cnt;
 44     stk.push(u);
 45     instack[u] = true;
 46     for(int i = head[u]; ~i; i = e[i].next){
 47         if(!dfn[e[i].to]){
 48             tarjan(e[i].to);
 49             low[u] = min(low[u],low[e[i].to]);
 50         }else if(instack[e[i].to]) low[u] = min(low[u],dfn[e[i].to]);
 51     }
 52     if(low[u] == dfn[u]){
 53         scc++;
 54         int v;
 55         do{
 56             v = stk.top();
 57             stk.pop();
 58             instack[v] = false;
 59             belong[v] = scc;
 60         }while(v != u);
 61     }
 62 }
 63 bool solve(){
 64     while(!stk.empty()) stk.pop();
 65     for(int i = 0; i < maxn; i++){
 66         belong[i] = dfn[i] = low[i] = 0;
 67         instack[i] = false;
 68     }
 69     scc = cnt = 0;
 70     for(int i = 0; i < n<<1; i++)
 71         if(!dfn[i]) tarjan(i);
 72     for(int i = 0; i < n; i++)
 73         if(belong[i<<1] == belong[i<<1|1]) return false;
 74     return true;
 75 }
 76 int main() {
 77     int x,y;
 78     double low,high,mid;
 79     while(~scanf("%d",&n)){
 80         for(int i = 0; i < n; i++)
 81             scanf("%d %d %d %d",&p[i<<1].x,&p[i<<1].y,&p[i<<1|1].x,&p[i<<1|1].y);
 82         low = 0;
 83         high = 2000.0;
 84         while(fabs(high - low) > exps){
 85             mid = (high + low)/2.0;
 86             memset(head,-1,sizeof(head));
 87             for(int i = tot = 0; i < (n-1)<<1; i++){
 88                 for(int j = i&1?i+1:i+2; j < n<<1; j++){
 89                     if(dis(p[i],p[j]) < 2.0*mid){//i与j不能共存
 90                         add(i,j^1);
 91                         add(j,i^1);
 92                     }
 93                 }
 94             }
 95             if(solve()) low = mid;
 96             else high = mid;
 97         }
 98         printf("%.2f\n",high);
 99     }
100     return 0;
101 }