【最大独立集】BZOJ3175- [Tjoi2013]攻击装置

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int MAXN=205;
 4 int n,maps[MAXN][MAXN];
 5 int lk[MAXN*MAXN],vis[MAXN*MAXN];
 6 vector<int> E[MAXN*MAXN];
 7 
 8 int check(int x,int y)
 9 {
10     if (x>=1 && x<=n && y>=1 && y<=n && maps[x][y]) return 1;else return 0;
11 }
12 
13 int id(int x,int y){return ((x-1)*n+y);}
14 
15 void addedge(int u,int v)
16 {
17     E[u].push_back(v);
18 }
19 
20 int find(int u)
21 {
22     for (int i=E[u].size()-1;i>=0;i--)
23     {
24         int v=E[u][i];
25         if (!vis[v])
26         {
27             vis[v]=1;
28             if (!lk[v]|| find(lk[v]))
29             {
30                 lk[v]=u;
31                 return 1;
32             }
33         }
34     }
35     return 0;
36 }
37 
38 void init()
39 {
40     scanf("%d",&n);
41     for (int i=1;i<=n;i++)
42     {
43         char str[MAXN];
44         scanf("%s",str);
45         for (int j=0;j<n;j++)
46             if (str[j]==‘0‘) maps[i][j+1]=1;else maps[i][j+1]=0;
47     }
48     for (int i=1;i<=n;i++)
49         for (int j=1;j<=n;j++)
50             if (maps[i][j]==1)
51             {
52                 if (check(i-1,j-2)) addedge(id(i,j),id(i-1,j-2));
53                 if (check(i-2,j-1)) addedge(id(i,j),id(i-2,j-1));
54                 if (check(i+1,j-2)) addedge(id(i,j),id(i+1,j-2));
55                 if (check(i+2,j-1)) addedge(id(i,j),id(i+2,j-1));
56                 if (check(i-1,j+2)) addedge(id(i,j),id(i-1,j+2));
57                 if (check(i-2,j+1)) addedge(id(i,j),id(i-2,j+1));
58                 if (check(i+1,j+2)) addedge(id(i,j),id(i+1,j+2));
59                 if (check(i+2,j+1)) addedge(id(i,j),id(i+2,j+1));
60             }
61 }
62 
63 void solve()
64 {
65     memset(lk,0,sizeof(lk));
66     int sum=0,ans=0;
67     for (int i=1;i<=n;i++)
68         for (int j=1;j<=n;j++)
69         {
70             if (maps[i][j]==1)
71             {
72                 int x=id(i,j);
73                 memset(vis,0,sizeof(vis));
74                 sum++;
75                 if (find(x)) ans++;
76             }
77         }
78     printf("%d",sum-ans/2);//不要忘记了除以2 
79 }
80 
81 int main()
82 {
83     init();
84     solve();
85 }