"POJ1815" Friendship network flow minimum cut

Test instructions: Several people, and then give the S, T, and the edge matrix, ask the least how many people to kill can let S and t these two (can not be killed) the person is not connected. (also the Minimum Dictionary order scheme)

Puzzle: Minimum cut, first we split, two parts of the flow to meet the nature, and then even the INF Unicom edge.

And then it's going to take a couple of people to run.

If it is INF, no answer

Then we from small to large enumeration which people in the smallest cut set inside, that is, the person deleted and then run, see Maxflow.

Then AC.

Note that in test instructions, if it is necessary to kill, the second line will output these people.

But do not say no need to do.

After detection, the output is not empty line, it is inferred that there is no such situation.

Code:

#include <cmath> #include <queue> #include <cstdio> #include <cstring> #include <iostream > #include <algorithm> #define N 2000//Network Diagram Midpoint # # G 1000000//Network Diagram Edge # define INF 0x3f3f3f3fusing namespace Std;s Truct ksd{int V,next,len;} E[g];int head[n],cnt;void Add (int u,int v,int len) {cnt++;e[cnt].v=v;e[cnt].len=len;e[cnt].next=head[u];head[u]=cnt;} Queue<int>q;int D[n],s,t;bool BFs () {memset (d,0,sizeof (d)); int I,u,v;while (!q.empty ()) Q.pop (); Q.push (s), D[s] =1;while (!q.empty ()) {U=q.front (), Q.pop (); for (I=head[u];i;i=e[i].next) if (E[i].len) {v=e[i].v;if (!d[v]) {D[v]=d[u] +1;if (v==t) return 1;q.push (v);}} return 0;} int dinic (int x,int flow) {if (x==t) return flow;int remain=flow,k;int i,v;for (i=head[x];i&&remain;i=e[i].next) {v=e[i].v;if (e[i].len&&d[v]==d[x]+1) {k=dinic (V,min (Remain,e[i].len)), if (!k) d[v]=0;e[i^1].len+=k,e[i]. Len-=k;remain-=k;}} return flow-remain;} int N,m,p,maxflow;int s,t,ans;int Map[1005][1005];bool vis[n];void build () {int I,j;cnt=1;memseT (head,0,sizeof (head)), for (i=1;i<=n;i++) if (!vis[i]) Add (i,i+n,1), add (i+n,i,0), for (i=1;i<=n;i++) if (!vis[i] ) for (j=1;j<=n;j++) if (!vis[j]) {if (i==j) continue;if (Map[i][j]) Add (I+n,j,inf), add (j,i+n,0);}} BOOL Work () {if (scanf ("%d%d%d", &n,&s,&t) ==eof) return 0;int i,j,k,flag=0;s=s+n,t=t;for (i=1;i<=n;i++) for (j=1;j<=n;j++) scanf ("%d", &map[i][j]), build (), Ans=0;while (BFS ()) {k=dinic (S,inf), if (K==inf) {puts ("NO Answer! "); return 1;} else ans+=k;} printf ("%d\n", ans), if (ans) flag=1;for (i=1;i<=n;i++) if (i!=s&&i!=t) {vis[i]=1;build (); Maxflow=0;while ( BFS ()) Maxflow+=dinic (S,inf), if (Maxflow<ans) printf ("%d", i), Ans=maxflow;else vis[i]=0;} Puts (""); return 1;} int main () {freopen ("test.in", "R", stdin), while (work ());}

"POJ1815" Friendship network flow minimum cut