URAL 1277 Cops and Thieves 最小割 无向图点带权点连通度

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 #define maxn 210
  4 int K, N, M, S, F;
  5 const int inf = 0x3f3f3f3f;
  6 struct Edge
  7 {
  8     int from, to, cap, flow;
  9     Edge(int f, int t, int c, int fl)
 10     {
 11         from = f; to = t; cap = c; flow = fl;
 12     }
 13 };
 14 vector <Edge> edges;
 15 vector <int> G[maxn];
 16 int n, m, s, t;
 17 int d[maxn], cur[maxn], vis[maxn];
 18 void AddEdge(int from, int to, int cap)
 19 {
 20     edges.push_back(Edge(from, to, cap, 0));
 21     edges.push_back(Edge(to, from, 0, 0));
 22     m = edges.size();
 23     G[from].push_back(m-2);
 24     G[to].push_back(m-1);
 25 }
 26 bool bfs()
 27 {
 28     memset(vis, 0, sizeof(vis));
 29     d[s] = 0;
 30     vis[s] = 1;
 31     queue <int> q;
 32     q.push(s);
 33     while(!q.empty())
 34     {
 35         int u = q.front(); q.pop();
 36         for(int i = 0; i < G[u].size(); i++)
 37         {
 38             Edge &e = edges[G[u][i]];
 39             if(!vis[e.to] && e.cap > e.flow)
 40             {
 41                 vis[e.to] = 1;
 42                 d[e.to] = d[u]+1;
 43                 q.push(e.to);
 44             }
 45         }
 46     }
 47     return vis[t];
 48 }
 49 int dfs(int x, int a)
 50 {
 51     if(x == t || a == 0) return a;
 52     int flow = 0, f;
 53     for(int &i = cur[x]; i < G[x].size(); i++)
 54     {
 55         Edge &e = edges[G[x][i]];
 56         if(d[x]+1 == d[e.to] && (f = dfs(e.to, min(e.cap-e.flow, a))) > 0)
 57         {
 58             e.flow += f;
 59             edges[G[x][i]^1].flow -= f;
 60             flow += f;
 61             a -= f;
 62             if(a == 0) break;
 63         }
 64     }
 65     return flow;
 66 }
 67 int MaxFlow()
 68 {
 69     int flow = 0;
 70     while(bfs())
 71     {
 72         memset(cur, 0, sizeof(cur));
 73         flow += dfs(s, inf);
 74     }
 75     return flow;
 76 }
 77 int main()
 78 {
 79     while(~scanf("%d", &K))
 80     {
 81         scanf("%d%d%d%d", &N, &M, &S, &F);
 82         s = F+N; t = S;
 83         edges.clear();
 84         for(int i = 1; i <= 2*N; i++) G[i].clear();
 85         
 86         for(int i = 1; i <= N; i++)
 87         {
 88             int temp; scanf("%d", &temp);
 89             AddEdge(i, N+i, temp);
 90         }
 91         for(int i = 1; i <= M; i++)
 92         {
 93             int a, b;
 94             scanf("%d%d", &a, &b);
 95             AddEdge(a+N, b, inf);
 96             AddEdge(b+N, a, inf);
 97         }
 98         int flow = MaxFlow();
 99 
100         if(flow <= K && S != F) printf("YES\n");
101         else printf("NO\n");
102     }
103     return 0;
104 }