【HDOJ6582】Path（最短路图，最小割）

题意：

 

 n,m<=1e4，c<=1e9

思路：

 

 

  1 #include<bits/stdc++.h>
  2 using namespace std;
  3 typedef long long ll;
  4 typedef unsigned int uint;
  5 typedef unsigned long long ull;
  6 typedef pair<int,int> PII;
  7 typedef pair<ll,ll> Pll;
  8 typedef vector<int> VI;
  9 #define N  110000
 10 #define M  1100000
 11 #define fi first
 12 #define se second
 13 #define MP make_pair
 14 #define pi acos(-1)
 15 #define mem(a,b) memset(a,b,sizeof(a))
 16 #define rep(i,a,b) for(int i=(int)a;i<=(int)b;i++)
 17 #define per(i,a,b) for(int i=(int)a;i>=(int)b;i--)
 18 #define lowbit(x) x&(-x)
 19 #define Rand (rand()*(1<<16)+rand())
 20 #define id(x) ((x)<=B?(x):m-n/(x)+1)
 21 #define ls p<<1
 22 #define rs p<<1|1
 23 
 24 const int MOD=1e9+7;
 25       double eps=1e-6;
 26       ll INF=1e14;
 27 
 28 priority_queue<pair<ll,int> > q;
 29 
 30 ll dis[N],dis1[N],dis2[N];
 31 int head[N],vet[N],nxt[N],len[N],vis[N],fan[N],gap[N],n,m,tot,S,T,s;
 32 
 33 struct arr
 34 {
 35     int x,y,z;
 36 }a[N];
 37 
 38 int read()
 39 {
 40    int v=0,f=1;
 41    char c=getchar();
 42    while(c<48||57<c) {if(c=='-') f=-1; c=getchar();}
 43    while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar();
 44    return v*f;
 45 }
 46 
 47 void add(int a,int b,int c)
 48 {
 49     nxt[++tot]=head[a];
 50     vet[tot]=b;
 51     len[tot]=c;
 52     head[a]=tot;
 53 }
 54 
 55 void Add(int a,int b,int c)
 56 {
 57     nxt[++tot]=head[a];
 58     vet[tot]=b;
 59     len[tot]=c;
 60     head[a]=tot;
 61 
 62     nxt[++tot]=head[b];
 63     vet[tot]=a;
 64     len[tot]=0;
 65     head[b]=tot;
 66 }
 67 
 68 void dijk(int st,int op)
 69 {
 70     mem(vis,0);
 71     rep(i,1,n) dis[i]=1e13;
 72     while(!q.empty()) q.pop();
 73     q.push(MP(0,st)); dis[st]=0;
 74     while(!q.empty())
 75     {
 76         int u=q.top().se;
 77         q.pop();
 78         if(vis[u]) continue;
 79         vis[u]=1;
 80         int e=head[u];
 81         while(e)
 82         {
 83             int v=vet[e];
 84             if(dis[u]+len[e]<dis[v])
 85             {
 86                 dis[v]=dis[u]+len[e];
 87                 q.push(MP(-dis[v],v));
 88             }
 89             e=nxt[e];
 90         }
 91     }
 92     if(op==1)
 93     {
 94         rep(i,1,n) dis1[i]=dis[i];
 95     }
 96      else
 97      {
 98          rep(i,1,n) dis2[i]=dis[i];
 99      }
100 }
101 
102 ll dfs(int u,int aug)
103 {
104     if(u==T) return aug;
105     int e=head[u],flow=0;
106     ll val=s-1;
107     while(e)
108     {
109         int v=vet[e];
110         if(len[e])
111         {
112             if(dis[u]==dis[v]+1)
113             {
114                 int t=dfs(v,min(len[e],aug-flow));
115                 len[e]-=t;
116                 len[fan[e]]+=t;
117                 flow+=t;
118                 if(dis[S]>=s) return flow;
119                 if(aug==flow) break;
120             }
121             val=min(val,dis[v]);
122         }
123         e=nxt[e];
124     }
125     if(!flow)
126     {
127         gap[dis[u]]--;
128         if(!gap[dis[u]]) dis[S]=s;
129         dis[u]=val+1;
130         gap[dis[u]]++;
131     }
132     return flow;
133 }
134 
135 
136 ll maxflow()
137 {
138     mem(gap,0);
139     mem(dis,0);
140     gap[0]=s;
141     ll ans=0;
142     while(dis[S]<s) ans+=dfs(S,INF);
143     return ans;
144 }
145 
146 int main()
147 {
148     //freopen("1.in","r",stdin);
149     //freopen("1.out","w",stdout);
150     rep(i,1,20000)
151      if(i&1) fan[i]=i+1;
152       else fan[i]=i-1;
153     int cas=read();
154     while(cas--)
155     {
156         n=read(),m=read();
157         rep(i,1,m)
158         {
159             a[i].x=read();
160             a[i].y=read();
161             a[i].z=read();
162         }
163         tot=0;
164         rep(i,1,n) head[i]=0;
165         rep(i,1,m) add(a[i].x,a[i].y,a[i].z);
166         dijk(1,1);
167         tot=0;
168         rep(i,1,n) head[i]=0;
169         rep(i,1,m) add(a[i].y,a[i].x,a[i].z);
170         dijk(n,2);
171         tot=0;
172         rep(i,1,n) head[i]=0;
173         rep(i,1,m)
174          if(dis1[a[i].x]+a[i].z+dis2[a[i].y]==dis1[n])
175           Add(a[i].x,a[i].y,a[i].z);
176 
177 
178         S=1; T=n; s=n;
179         ll ans=maxflow();
180         printf("%I64d\n",ans);
181     }
182     return 0;
183 }

 

posted on 2019-08-31 13:29  myx12345  阅读(345)  评论(0)  编辑  收藏  举报

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