Codeforces 325D

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <ctime>
 6 #include <cmath>
 7 #include <map>
 8 #include <set>
 9 using namespace std;
10
11 const int maxn=3000*3000*2+100;
12 const int dx[8]={-1, -1, -1, 0, 0, 1, 1, 1};
13 const int dy[8]={-1, 0, 1, -1, 1, -1, 0, 1};
14
15 int n, r, c, ti;
16 int ans;
17 int fa[maxn];
18 bool vis[3010][6010];
19 int mark[maxn];
20
21 int find(int cur)
22 {
23     if (fa[cur]<0) return cur;
24     else return (find(fa[cur]));
25 }
26 void Union(int u, int v)
27 {
28     u=find(u);
29     v=find(v);
30     if (u==v) return;
31     if (fa[u]>fa[v]) swap(u, v);
32     fa[u]+=fa[v];
33     fa[v]=u;
34 }
35 bool check(int &x1, int &y1)
36 {
37     if (x1<1 || x1>r) return false;
38     if (y1==0) y1=c;
39     else if (y1>c) y1=1;
40     if (!vis[x1][y1]) return false;
41     return true;
42 }
43 void merge(int x, int y)
44 {
45     int nid=(x-1)*c+y;
46     for (int i=0; i<8; ++i)
47     {
48         int x1=x+dx[i];
49         int y1=y+dy[i];
50         if (check(x1, y1)) Union(nid, (x1-1)*c+y1);
51     }
52 }
53 bool get_list(int x, int y, int id)
54 {
55     for (int i=0; i<8; ++i)
56     {
57         int x1=x+dx[i];
58         int y1=y+dy[i];
59         if (!check(x1, y1)) continue;
60         int tmp=find((x1-1)*c+y1);
61         if (id && mark[tmp]==ti-1) return false;
62         mark[tmp]=ti;
63     }
64     return true;
65 }
66 void solve()
67 {
68     if (c==1) return;
69     c*=2;
70
71     for (int i=1; i<=r; ++i)
72         for (int j=1; j<=c; ++j)
73             fa[(i-1)*c+j]=-1;
74
75     for (int i=1; i<=n; ++i)
76     {
77         int x, y;
78         scanf("%d%d", &x, &y);
79         ++ti;
80         get_list(x, y, 0);
81         ++ti;
82         bool flag=get_list(x, y+c/2, 1);
83         if (!flag) continue;
84         ++ans;
85         merge(x, y);
86         merge(x, y+c/2);
87         vis[x][y]=true;
88         vis[x][y+c/2]=true;
89     }
90 }
91 int main()
92 {
93     freopen("input.txt", "r", stdin);
94     freopen("output.txt", "w", stdout);
95     scanf("%d%d%d", &r, &c, &n);
96     solve();
97     printf("%d\n", ans);
98     return 0;
99 }