HDU2444-The Accomodation of Students-判断是否为二分图+ISAP

要先判断是不是二分图。用黑白染色法。

遇到已经染过的跟当前的颜色相同时就说明不是二分图，也即出现了奇环

 /*--------------------------------------------------------------------------------------*/

 #include <algorithm>
 #include <iostream>
 #include <cstring>
 #include <ctype.h>
 #include <cstdlib>
 #include <cstdio>
 #include <vector>
 #include <string>
 #include <queue>
 #include <stack>
 #include <cmath>
 #include <set>
 #include <map>

 //debug function for a N*M array
 #define debug_map(N,M,G) printf("\n");for(int i=0;i<(N);i++)\
 {for(int j=;j<(M);j++){\
 printf("%d",G[i][j]);}printf("\n");}
 //debug function for int,float,double,etc.
 #define debug_var(X) cout<<#X"="<<X<<endl;
 #define LL long long
 const int INF = 0x3f3f3f3f;
 const LL LLINF = 0x3f3f3f3f3f3f3f3f;
 /*--------------------------------------------------------------------------------------*/
 using namespace std;

 int N,M,T;

 const int maxn = ;
 const int maxm = ;
 struct Edge{
     int to,next;
 }edge[maxm];

 int head[maxn],tot;
 void init()
 {
     tot = ;
     memset(head,-,sizeof head);
 }
 void add_edge(int u,int v)
 {
     edge[tot].to = v;edge[tot].next = head[u];
     head[u] = tot++;
 }

 int linker[maxn];
 bool used[maxn];
 int uN;

 bool dfs(int u)
 {
     for(int i=head[u];~i;i=edge[i].next)
     {
         int v = edge[i].to;
         if(!used[v])
         {
             used[v] = true;
             if(linker[v] == - || dfs(linker[v]))
             {
                 linker[v] = u;
                 return true;
             }
         }
     }
     return false;
 }
 int hungary()
 {
     int res = ;
     memset(linker,-,sizeof linker);
     for(int u=;u<=uN;u++)
     {
         memset(used,false,sizeof used);
         if(dfs(u)) res++;
     }
     return res/;
 }

 int col[maxn];
 bool isBipartite(int u)
 {
     queue<int> Q;
     Q.push(u);
     col[u] = ;
     while(!Q.empty())
     {
         int cur = Q.front();Q.pop();
         for(int i = head[cur];~i;i=edge[i].next)
         {
             int v = edge[i].to;
             if(col[v] == col[cur]) return false;
             if(col[v] != -) continue;
             col[v] = !col[cur];
             Q.push(v);
         }
     }
     return true;
 }

 int main()
 {
     while(~scanf("%d%d",&N,&M))
     {
         init();
         uN = N;
         for(int i=,u,v;i<M;i++)
         {
             scanf("%d%d",&u,&v);
             add_edge(u,v);
             add_edge(v,u);
         }

         bool flag = true;
         memset(col,-,sizeof col);
         for(int i=;i<=uN;i++) if(col[i] == -)
         {
             if(!isBipartite(i) ){flag = false;break;}
         }
         if(flag)
         {
             printf("%d\n",hungary());
         }
         else printf("No\n");

     }
 }