HDU-1532 网络流裸题

HDU-1532

题意简单的来说就是从1点到n点，最大的流量是多少。

代码：

 #include<bits/stdc++.h>
 using namespace std;
 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 #define LL long long
 #define ULL unsigned LL
 #define fi first
 #define se second
 #define pb push_back
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 #define max3(a,b,c) max(a,max(b,c))
 #define min3(a,b,c) min(a,min(b,c))
 #define _S(X) cout << x << ' ';
 #define __S(x) cout << x << endl;
 typedef pair<int,int> pll;
 const int INF = 0x3f3f3f3f;
 const LL mod =  (int)1e9+;
 const int N = ;
 int head[N], w[N], to[N], nx[N];
 int n, m, _u, _v, _w;
 int tot, s, t;
 int deep[N];
 void add(int u, int v, int val){
     w[tot]  = val;
     to[tot] = v;
     nx[tot] = head[u];
     head[u] = tot++;
 }

 void init(){
     memset(head, -, sizeof(head));
     tot = ;
     s = ;
     t = n;
 }

 int bfs(){
     queue<int> q;
     memset(deep, , sizeof(deep));
     q.push(s);
     deep[s] = ;
     while(!q.empty()){
         int u = q.front();
         q.pop();
         for(int i = head[u]; ~i; i = nx[i]){
             if(w[i] >  && deep[to[i]] == ){
                 deep[to[i]] = deep[u] + ;
                 q.push(to[i]);
             }
         }
     }
     if(deep[t] > ) return ;
     return ;
 }
 int Dinic(int u, int flow){
     if(u == t) return flow;
     for(int i = head[u]; ~i; i = nx[i]){
         if(deep[u]+ == deep[to[i]] && w[i] > ){
             int di = Dinic(to[i], min(w[i], flow));
             if(di > ){
                 w[i] -= di, w[i^] += di;
                 return di;
             }
         }
     }
     return ;
 }
 int main(){
     while(~scanf("%d%d", &m, &n)){
         init();
         for(int i = ; i <= m; i++){
             scanf("%d%d%d", &_u, &_v, &_w);
             add(_u, _v, _w);
             add(_v, _u, );
         }
         s = ; t = n;
         int ans = , tmp;
         while(bfs()){
             while(tmp = Dinic(s, INF)) ans += tmp;
         }
         printf("%d\n", ans);
     }
     return ;
 }

Dinic 还可以用当前弧优化，记录了当前处理到那一条边，就不需要重头再遍历那些l边。

 #include<bits/stdc++.h>
 using namespace std;
 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 #define LL long long
 #define ULL unsigned LL
 #define fi first
 #define se second
 #define pb push_back
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 #define max3(a,b,c) max(a,max(b,c))
 #define min3(a,b,c) min(a,min(b,c))
 #define _S(X) cout << x << ' ';
 #define __S(x) cout << x << endl;
 typedef pair<int,int> pll;
 const int INF = 0x3f3f3f3f;
 const LL mod =  (int)1e9+;
 const int N = ;
 int head[N], w[N], to[N], nx[N];
 int n, m, _u, _v, _w;
 int tot, s, t;
 int deep[N], cur[N];
 void add(int u, int v, int val){
     w[tot]  = val;
     to[tot] = v;
     nx[tot] = head[u];
     head[u] = tot++;
 }

 void init(){
     memset(head, -, sizeof(head));
     tot = ;
     s = ;
     t = n;
 }

 int bfs(){
     queue<int> q;
     memset(deep, , sizeof(deep));
     q.push(s);
     deep[s] = ;
     while(!q.empty()){
         int u = q.front();
         q.pop();
         for(int i = head[u]; ~i; i = nx[i]){
             if(w[i] >  && deep[to[i]] == ){
                 deep[to[i]] = deep[u] + ;
                 q.push(to[i]);
             }
         }
     }
     if(deep[t] > ) return ;
     return ;
 }
 int Dinic(int u, int flow){
     if(u == t) return flow;
     for(int &i = cur[u]; ~i; i = nx[i]){
         if(deep[u]+ == deep[to[i]] && w[i] > ){
             int di = Dinic(to[i], min(w[i], flow));
             if(di > ){
                 w[i] -= di, w[i^] += di;
                 return di;
             }
         }
     }
     return ;
 }
 int main(){
     while(~scanf("%d%d", &m, &n)){
         init();
         for(int i = ; i <= m; i++){
             scanf("%d%d%d", &_u, &_v, &_w);
             add(_u, _v, _w);
             add(_v, _u, );
         }
         s = ; t = n;
         int ans = , tmp;
         while(bfs()){
             for(int i = ; i <= n; i++) cur[i] = head[i];
             while(tmp = Dinic(s, INF)) ans += tmp;
         }
         printf("%d\n", ans);
     }
     return ;
 }

当前弧优化

 #include<bits/stdc++.h>
 using namespace std;
 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 #define LL long long
 #define ULL unsigned LL
 #define fi first
 #define se second
 #define pb push_back
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 #define max3(a,b,c) max(a,max(b,c))
 #define min3(a,b,c) min(a,min(b,c))
 #define _S(X) cout << x << ' ';
 #define __S(x) cout << x << endl;
 typedef pair<int,int> pll;
 const int INF = 0x3f3f3f3f;
 const LL mod =  (int)1e9+;
 const int N = ;
 int head[N], w[N], to[N], nx[N];
 int vis[N], pre[N], id[N];
 int n, m, _u, _v, _w;
 int tot, s, t;
 void add(int u, int v, int val){
     w[tot]  = val;
     to[tot] = v;
     nx[tot] = head[u];
     head[u] = tot++;
 }

 void init(){
     memset(head, -, sizeof(head));
     tot = ;
     s = ;
     t = n;
 }

 int bfs(){
     queue<int> q;
     memset(vis, , sizeof(vis));
     q.push(s);
     vis[s] = ;
     pre[s] = s;
     while(!q.empty()){
         int u = q.front();
         q.pop();
         for(int i = head[u]; ~i; i = nx[i]){
             if(!vis[to[i]] && w[i]){
                 pre[to[i]] = u;
                 id[to[i]] = i;
                 vis[to[i]] = ;
                 if(to[i] == t) return true;
                 q.push(to[i]);
             }
         }
     }
     return false;
 }
 int EK(){
     int ans = ;
     while(bfs()){
         int mi = INF;
         for(int i = t; i != s; i = pre[i]){
             mi = min(mi, w[id[i]]);
         }
         for(int i = t; i != s; i = pre[i]){
             w[id[i]] -= mi;
             w[id[i]^] += mi;
         }
         ans += mi;
     }
     return ans;
 }
 int main(){
     while(~scanf("%d%d", &m, &n)){
         init();
         for(int i = ; i <= m; i++){
             scanf("%d%d%d", &_u, &_v, &_w);
             add(_u, _v, _w);
             add(_v, _u, );
         }
         s = ; t = n;
         printf("%d\n", EK());
     }
     return ;
 }

EK