UVA1184 Air Raid

嘟嘟嘟

最小路径覆盖板子题。

建二分图，然后跑Dinic（因为我不会匈牙利），然后ans = n - maxflow()。

主要是发一下用链前存图的写法。(好像比vector短一点)

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a, x) memset(a, x, sizeof(a))
 #define rg register
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = 1e5 + ;
 inline ll read()
 {
   ll ans = ;
   char ch = getchar(), last = ' ';
   while(!isdigit(ch)) {last = ch; ch = getchar();}
   while(isdigit(ch)) {ans = ans *  + ch - ''; ch = getchar();}
   if(last == '-') ans = -ans;
   return ans;
 }
 inline void write(ll x)
 {
   if(x < ) x = -x, putchar('-');
   if(x >= ) write(x / );
   putchar(x %  + '');
 }

 int n, m, t;
 struct Edge
 {
   int nxt, from, to, cap, flow;
 }e[maxn << ];
 int head[maxn << ], ecnt = ;  //初值一定是奇数，否则^1不是他的反向边！
 void addEdge(int x, int y)
 {
   e[++ecnt] = (Edge){head[x], x, y, , };
   head[x] = ecnt;
   e[++ecnt] = (Edge){head[y], y, x, , };
   head[y] = ecnt;
 }

 int dis[maxn];
 bool bfs()
 {
   Mem(dis, ); dis[] = ;
   queue<int> q; q.push();
   while(!q.empty())
     {
       int now = q.front(); q.pop();
       for(int i = head[now]; i; i = e[i].nxt)
       if(!dis[e[i].to] && e[i].cap > e[i].flow)
         {
           dis[e[i].to] = dis[now] + ;
           q.push(e[i].to);
         }
     }
   return dis[t];
 }
 int cur[maxn];
 int dfs(int now, int res)
 {
   if(now == t || res == ) return res;
   int flow = , f;
   if(!cur[now]) cur[now] = head[now];
   for(int &i = cur[now]; i; i = e[i].nxt)
     {
       if(dis[e[i].to] == dis[now] +  && (f = dfs(e[i].to, min(res, e[i].cap - e[i].flow))) > )
     {
       e[i].flow += f; e[i ^ ].flow -= f;
       flow += f; res -= f;
       if(res == ) break;
     }
     }
   return flow;
 }

 int maxflow()
 {
   int flow = ;
   while(bfs())
     {
       Mem(cur, );
       flow += dfs(, INF);
     }
   return flow;
 }

 void init()
 {
   Mem(head, ); ecnt = ;
 }

 int main()
 {
   int T = read();
   while(T--)
     {
       n = read(); m = read(); t = n + n + ;
       init();
       for(int i = ; i <= n; ++i) addEdge(, i), addEdge(i + n, t);
       for(int i = ; i <= m; ++i)
     {
       int x = read(), y = read();
       addEdge(x, y + n);
     }
       write(n - maxflow()); enter;
     }
   return ;
 }