zoj 2760 最短路+网络流

题意：求一个有向图起点到终点的边不相交的最短路径的条数。

思路：曾经一个求最短路的类似，这题你找出来所有的最短路所包含的边就可以，然后跑一边网络流即可

#include<bits/stdc++.h>
using namespace std;
const int maxn=400;
const int maxm=160000;
const int inf=0x3f3f3f3f;
int mapp[maxn][maxn];
struct edge
{
    int v,w,nxt;
}edge[maxm*4];
int head[maxn],cnt;
void add_edge(int u,int v,int w)
{
    edge[cnt].v=v;
    edge[cnt].w=w;
    edge[cnt].nxt=head[u];
    head[u]=cnt++;
    edge[cnt].v=u;
    edge[cnt].w=0;
    edge[cnt].nxt=head[v];
    head[v]=cnt++;
}
int dis[maxn];
int diss[maxn][maxn];
int vis[maxn];
int numh[maxn],h[maxn],curedge[maxn],pre[maxn];
int sap(int s,int t,int n)
{
    memset(numh,0,sizeof(numh));
    memset(h,0,sizeof(h));
    memset(pre,-1,sizeof(pre));
    int cur_flow,flow_ans=0,u,tmp,neck,i;
    for(i=1;i<=n;i++)
    {
        curedge[i]=head[i];
    }
    numh[0]=n;
    u=s;
    while(h[s]<n)
    {
        //printf("%d\n",h[s]);
        //printf("1111\n");
        if(u==t)
        {
            cur_flow=inf;
            for(i=s;i!=t;i=edge[curedge[i]].v)
            {
                if(cur_flow>edge[curedge[i]].w)
                {
                    neck=i;
                    cur_flow=edge[curedge[i]].w;
                }
            }
            for(i=s;i!=t;i=edge[curedge[i]].v)
            {
                tmp=curedge[i];
                edge[tmp].w-=cur_flow;
                edge[tmp^1].w+=cur_flow;
            }
            flow_ans+=cur_flow;
            u=neck;
        }
        for(i=curedge[u];i!=-1;i=edge[i].nxt)
        {
            if(edge[i].w&&h[u]==h[edge[i].v]+1)
            {
                break;
            }
        }
        if(i!=-1)
        {
            curedge[u]=i;
            pre[edge[i].v]=u;
            u=edge[i].v;
        }
        else
        {
            if(0==--numh[h[u]])
                break;
            curedge[u]=head[u];
            for(tmp=n,i=head[u];i!=-1;i=edge[i].nxt)
            {
                if(edge[i].w)
                {
                    tmp=min(tmp,h[edge[i].v]);
                }
            }
            h[u]=tmp+1;
            ++numh[h[u]];
            if(u!=s)
                u=pre[u];
        }
    }
    return flow_ans;
}
int main ()
{
    int n;
    while(~scanf("%d",&n))
    {
        memset(head,-1,sizeof(head));
        cnt=0;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                scanf("%d",&mapp[i][j]);
                if(mapp[i][j]<0)
                    mapp[i][j]=inf;
                if(i==j)
                    mapp[i][j]=0;
                diss[i][j]=mapp[i][j];
            }
        }
        for(int k=1;k<=n;k++)
        {
            for(int i=1;i<=n;i++)
            {
                for(int j=1;j<=n;j++)
                {
                    if((mapp[i][j]>mapp[i][k]+mapp[k][j]||mapp[i][j]>inf)&&mapp[i][k]<inf&&mapp[k][j]<inf)
                        mapp[i][j]=mapp[i][k]+mapp[k][j];
                }
            }
        }
        int s,t;
        scanf("%d%d",&s,&t);
        s++,t++;
        if(n==1||s==t)
        {
            printf("inf\n");
            continue;
        }
        if(mapp[s][t]>=inf)
        {
            printf("0\n");
            continue;
        }
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                if(mapp[i][j]<inf&&diss[i][j]<inf&&mapp[s][i]+mapp[j][t]+diss[i][j]==mapp[s][t])
                {
                    add_edge(i,j,1);
                    //printf("%d %d\n",i,j);
                }
            }
        }
       int res=sap(s,t,n);
       printf("%d\n",res);
    }
    return 0;
}