HDOJ 3622 Bomb Game 2-sat

  1 #include<cstdio>
  2 #include<algorithm>
  3 #include<cstring>
  4 #include<cmath>
  5 using namespace std;
  6 
  7 struct E
  8 {
  9     int next, y;
 10 } edge[40010];
 11 int col[210], dfn[210], low[210], stack[210], en[210], x[210], y[210];
 12 int esize, n, top, ti1, cnt;
 13 double d[210][210];
 14 const double eps = 1e-8;
 15 void insert(int u, int v)
 16 {
 17     edge[++esize].y = v;
 18     edge[esize].next = en[u];
 19     en[u] = esize;
 20 }
 21 void dfs(int x)
 22 {
 23     //printf("%d %d\n", x, time);
 24     dfn[x] = low[x] = ti1 ++;
 25     stack[top++] = x;
 26     for (int t = en[x]; t != -1; t = edge[t].next)
 27     {
 28         int y = edge[t].y;
 29         if (dfn[y] == -1){
 30             dfs(y);
 31             if (low[y] < low[x]) low[x] = low[y];
 32         }
 33         else if (col[y] == -1 && low[y] < low[x]){  //low[y] can be replaced by dfn[y], equal? not equal but make no difference to scc
 34             low[x] = low[y];
 35         }
 36     }
 37     if (dfn[x] == low[x])
 38     {
 39         cnt ++;
 40         while(stack[--top] != x) col[stack[top]] = cnt;
 41         col[x] = cnt;
 42     }
 43 }
 44 bool ok(double r)
 45 {
 46     //new map
 47     memset(en, -1, sizeof(en));
 48     esize = 0;
 49     for (int i = 0; i < n; i++)
 50         for (int j = i + 1; j < n; j++)
 51         {
 52             if (d[i][j] < r * 2.0){
 53                 insert(i, j + n);
 54                 insert(j, i + n);
 55             }
 56             if (d[i][j+n] < r * 2.0){
 57                 insert(i, j);
 58                 insert(j + n, i + n);
 59             }
 60             if (d[i+n][j] < r * 2.0){
 61                 insert(i + n, j + n);
 62                 insert(j, i);
 63             }
 64             if (d[i+n][j+n] < r * 2.0){
 65                 insert(j + n, i);
 66                 insert(i + n, j);
 67             }
 68         }
 69     //printf("r is %lf, esize is %d\n", r, esize);
 70     //tarjan dfs
 71     memset(col, -1, sizeof(col));
 72     memset(low, -1, sizeof(low));
 73     memset(dfn, -1, sizeof(dfn));
 74     top = 0; ti1 = 0; cnt = 0;
 75     for (int i = 0; i < 2 * n; i++)
 76         if (dfn[i] == -1) dfs(i);
 77     //judge
 78     //for (int i = 0; i < n; i++)
 79     //    printf("color: %d %d %d\n", i, col[i], col[i+n]);
 80     for (int i = 0; i < n; i++)
 81         if (col[i] == col[i + n]) {
 82         //    printf("%d", col[i]);
 83             return false;}
 84     return true;
 85 }
 86 double dis(int i, int j)
 87 {
 88     return sqrt(double(x[i] - x[j]) * double(x[i] - x[j]) +
 89             double(y[i] - y[j]) * double(y[i] - y[j]));
 90 }
 91 int main()
 92 {
 93     while(scanf("%d", &n) != EOF)
 94     {
 95         double max = 0;
 96         for (int i = 0; i < n; i++)
 97         {
 98             scanf("%d%d%d%d", &x[i], &y[i], &x[i+n], &y[i+n]);
 99         }
100         for (int i = 0; i < n; i++)
101             for (int j = i + 1; j < n; j++)
102             {
103                 d[i][j] = d[j][i] = dis(i, j);
104                 if (d[i][j] > max) max = d[i][j];
105                 d[j][i+n] = d[i+n][j] = dis(i+n, j);
106                 if (d[i+n][j] > max) max = d[i+n][j];
107                 d[i][j+n] = d[j+n][i] = dis(i, j+n);
108                 if (d[i][j+n] > max) max = d[i][j+n];
109                 d[i+n][j+n] = d[j+n][i+n] = dis(i+n, j+n);
110                 if (d[i+n][j+n] > max) max = d[i+n][j+n];
111             }
112     //    for (int i = 0; i < n; i++)
113     //        for (int j = i + 1; j < n; j++)
114     //        {
115     //            printf("%lf %lf %lf %lf\n", d[i][j], d[i][j+n], d[i+n][j], d[i+n][j+n]);
116     //        }
117         double l = 0.0, r = max, ans = 0.0;
118         while (l + eps <= r)
119         {
120     //        puts("yes");
121             double mid = (l + r) / 2.0;
122     //        printf("%lf\n", mid);
123             if (ok(mid))
124             {
125     //            printf("%lf is ok\n", mid);
126                 if (mid > ans)
127                     ans = mid;
128                 l = mid + eps;
129             }
130             else
131                 r = mid - eps;
132         }
133         printf("%.2lf\n", ans);
134     }
135     return 0;
136 }