51nod 1442 士兵的旅行

拆点，因为只能走一步，那么u->v 后就不能到k了，这样，建图就能保证只走一步；

  1 #include <bits/stdc++.h>
  2
  3 using namespace std;
  4
  5 const int maxn = 105*2;
  6 const int INF = 0x3f3f3f3f;
  7
  8 struct Edge {
  9     int from,to,cap,flow;
 10 };
 11
 12 struct Dinic
 13 {
 14     int n,m,s,t;
 15     vector<Edge> edge;
 16     vector<int> G[maxn];
 17     bool vis[maxn];
 18     int d[maxn];
 19     int cur[maxn];
 20
 21     void init()
 22     {
 23         for(int i=0;i<maxn;i++)
 24             G[i].clear();
 25         edge.clear();
 26         memset(d,0,sizeof(d));
 27         memset(vis,0,sizeof(vis));
 28         memset(cur,0,sizeof(cur));
 29     }
 30
 31     void addEdge (int from,int to,int cap)
 32     {
 33         edge.push_back((Edge){from,to,cap,0});
 34         edge.push_back((Edge){to,from,0,0});
 35         m = edge.size();
 36         G[from].push_back(m-2);
 37         G[to].push_back(m-1);
 38     }
 39
 40     bool BFS()
 41     {
 42         memset(vis,0,sizeof(vis));
 43         queue<int> Q;
 44         Q.push(s);
 45         d[s] = 0;
 46         vis[s] = 1;
 47         while(!Q.empty())
 48         {
 49             int x = Q.front();
 50             Q.pop();
 51             for(int i=0; i<G[x].size(); i++)
 52             {
 53                 Edge & e = edge[G[x][i]];
 54                 if(!vis[e.to]&&e.cap>e.flow)
 55                 {
 56                     vis[e.to] = 1;
 57                     d[e.to] = d[x] + 1;
 58                     Q.push(e.to);
 59                 }
 60             }
 61         }
 62         return vis[t];
 63     }
 64
 65     int DFS(int x,int a)
 66     {
 67         if(x==t||a==0) return a;
 68         int flow = 0,f;
 69         for(int & i = cur[x]; i<G[x].size(); i++)
 70         {
 71             Edge & e = edge[G[x][i]];
 72             if(d[x] + 1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
 73             {
 74                 e.flow +=f;
 75                 edge[G[x][i]^1].flow -=f;
 76                 flow +=f;
 77                 a-=f;
 78                 if(a==0) break;
 79             }
 80         }
 81         return flow;
 82     }
 83
 84     int Maxflow (int s,int t) {
 85         this->s = s;this->t = t;
 86         int flow = 0;
 87         while(BFS()) {
 88             memset(cur,0,sizeof(cur));
 89             flow+=DFS(s,INF);
 90         }
 91         return flow;
 92     }
 93
 94 }sol;
 95
 96
 97 int main()
 98 {
 99     int n,m;
100     scanf("%d%d",&n,&m);
101
102     int s = 0;
103     int t = 2*n+1;
104
105     sol.init();
106     int sum = 0;
107     for(int i=1;i<=n;i++) {
108         int a;
109         scanf("%d",&a);
110         sum +=a;
111         sol.addEdge(s,i,a);
112         sol.addEdge(i,i+n,INF);
113     }
114
115     int sum2 = 0;
116     for(int i=1;i<=n;i++) {
117         int a;
118         scanf("%d",&a);
119         sum2+=a;
120         sol.addEdge(i+n,t,a);
121     }
122
123     for(int i=0;i<m;i++) {
124         int u,v;
125         scanf("%d%d",&u,&v);
126         sol.addEdge(u,v+n,INF);
127         sol.addEdge(v,u+n,INF);
128     }
129
130     int ans = sol.Maxflow(s,t);
131     if(ans==sum&&sum2==sum)
132         puts("YES");
133     else puts("NO");
134
135     return 0;
136 }