P1330-封锁阳光大学 

 1 #include <bits/stdc++.h>
 2 #define _for(i,a,b) for(int i = (a);i < b;i ++)
 3 #define _rep(i,a,b) for(int i = (a);i > b;i --)
 4 #define INF 0x3f3f3f3f
 5 #define pb push_back
 6 typedef long long ll;
 7 using namespace std;
 8 inline ll read()
 9 {
10     ll ans = 0;
11     char ch = getchar(), last = ' ';
12     while(!isdigit(ch)) last = ch, ch = getchar();
13     while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
14     if(last == '-') ans = -ans;
15     return ans;
16 }
17 inline void write(ll x)
18 {
19     if(x < 0) x = -x, putchar('-');
20     if(x >= 10) write(x / 10);
21     putchar(x % 10 + '0');
22 }
23 
24 #define pb push_back
25 const int maxn = 100003; 
26 vector<int> G[maxn];
27 int ans = 0;
28 int V;
29 int color[maxn];
30 int a,b;
31 bool dfs(int v,int c)
32 {
33     color[v] = c;
34     if(c==1)
35         a ++;
36     else
37         b ++;
38     for(int i = 0;i < G[v].size();i ++)
39     {
40         if(color[G[v][i]] == c) return false;
41         if(color[G[v][i]] == 0 && !dfs(G[v][i],-c)) return false;
42     }
43     return true;
44 }
45 int biGraph()
46 {
47     memset(color,0,sizeof(color));
48     for(int i = 1;i < V+1;i ++)
49     {
50         a = 0,b = 0;
51         if(color[i]==0)
52             if(!dfs(i,1))
53                 return 0;
54         ans += min(a,b);
55     }
56     return 1;
57 }
58 int M;
59 
60 int main()
61 {
62     V = read();
63     M = read();
64     
65      _for(i,0,M)
66     {
67         int a = read(),b = read();
68         G[a].pb(b);
69         G[b].pb(a);
70     }
71     
72     int rnt = biGraph();
73     int rnt1 = 0,rnt2 = 0;
74     if(!rnt)
75     {
76         printf("Impossible\n");
77         return 0;
78     }
79     else
80         printf("%d\n",ans);
81     
82     return 0;
83 }

 

posted @ 2019-09-11 09:18  Asurudo  阅读(115)  评论(0)    收藏  举报