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

Posted 2020-08-05 Helica

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

  1 /*--------------------------------------------------------------------------------------*/
  2 
  3 #include <algorithm>
  4 #include <iostream>
  5 #include <cstring>
  6 #include <ctype.h>
  7 #include <cstdlib>
  8 #include <cstdio>
  9 #include <vector>
 10 #include <string>
 11 #include <queue>
 12 #include <stack>
 13 #include <cmath>
 14 #include <set>
 15 #include <map>
 16 
 17 //debug function for a N*M array
 18 #define debug_map(N,M,G) printf("\n");for(int i=0;i<(N);i++) 19 {for(int j=0;j<(M);j++){ 20 printf("%d",G[i][j]);}printf("\n");}
 21 //debug function for int,float,double,etc.
 22 #define debug_var(X) cout<<#X"="<<X<<endl;
 23 #define LL long long
 24 const int INF = 0x3f3f3f3f;
 25 const LL LLINF = 0x3f3f3f3f3f3f3f3f;
 26 /*--------------------------------------------------------------------------------------*/
 27 using namespace std;
 28 
 29 int N,M,T;
 30 
 31 const int maxn = 300;
 32 const int maxm = 30000;
 33 struct Edge{
 34     int to,next;
 35 }edge[maxm];
 36 
 37 int head[maxn],tot;
 38 void init()
 39 {
 40     tot = 0;
 41     memset(head,-1,sizeof head);
 42 }
 43 void add_edge(int u,int v)
 44 {
 45     edge[tot].to = v;edge[tot].next = head[u];
 46     head[u] = tot++;
 47 }
 48 
 49 int linker[maxn];
 50 bool used[maxn];
 51 int uN;
 52 
 53 bool dfs(int u)
 54 {
 55     for(int i=head[u];~i;i=edge[i].next)
 56     {
 57         int v = edge[i].to;
 58         if(!used[v])
 59         {
 60             used[v] = true;
 61             if(linker[v] == -1 || dfs(linker[v]))
 62             {
 63                 linker[v] = u;
 64                 return true;
 65             }
 66         }
 67     }
 68     return false;
 69 }
 70 int hungary()
 71 {
 72     int res = 0;
 73     memset(linker,-1,sizeof linker);
 74     for(int u=1;u<=uN;u++)
 75     {
 76         memset(used,false,sizeof used);
 77         if(dfs(u)) res++;
 78     }
 79     return res/2;
 80 }
 81 
 82 int col[maxn];
 83 bool isBipartite(int u)
 84 {
 85     queue<int> Q;
 86     Q.push(u);
 87     col[u] = 1;
 88     while(!Q.empty())
 89     {
 90         int cur = Q.front();Q.pop();
 91         for(int i = head[cur];~i;i=edge[i].next)
 92         {
 93             int v = edge[i].to;
 94             if(col[v] == col[cur]) return false;
 95             if(col[v] != -1) continue;
 96             col[v] = !col[cur];
 97             Q.push(v);
 98         }
 99     }
100     return true;
101 }
102 
103 int main()
104 {
105     while(~scanf("%d%d",&N,&M))
106     {
107         init();
108         uN = N;
109         for(int i=0,u,v;i<M;i++)
110         {
111             scanf("%d%d",&u,&v);
112             add_edge(u,v);
113             add_edge(v,u);
114         }
115 
116         bool flag = true;
117         memset(col,-1,sizeof col);
118         for(int i=1;i<=uN;i++) if(col[i] == -1)
119         {
120             if(!isBipartite(i) ){flag = false;break;}
121         }
122         if(flag)
123         {
124             printf("%d\n",hungary());
125         }
126         else printf("No\n");
127 
128     }
129 }