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：

 1 #include
 2 using namespace std;
 3 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 4 #define LL long long
 5 #define ULL unsigned LL
 6 #define fi first
 7 #define se second
 8 #define pb push_back
 9 #define lson l,m,rt<<1
10 #define rson m+1,r,rt<<1|1
11 #define max3(a,b,c) max(a,max(b,c))
12 #define min3(a,b,c) min(a,min(b,c))
13 #define _S(X) cout << x << ' ';
14 #define __S(x) cout << x << endl;
15 typedef pair<int,int> pll;
16 const int INF = 0x3f3f3f3f;
17 const LL mod =  (int)1e9+7;
18 const int N = 405;
19 int head[N], w[N], to[N], nx[N];
20 int n, m, _u, _v, _w;
21 int tot, s, t;
22 int deep[N];
23 void add(int u, int v, int val){
24     w[tot]  = val;
25     to[tot] = v;
26     nx[tot] = head[u];
27     head[u] = tot++;
28 }
29 
30 void init(){
31     memset(head, -1, sizeof(head));
32     tot = 0;
33     s = 1;
34     t = n;
35 }
36 
37 int bfs(){
38     queue<int> q;
39     memset(deep, 0, sizeof(deep));
40     q.push(s);
41     deep[s] = 1;
42     while(!q.empty()){
43         int u = q.front();
44         q.pop();
45         for(int i = head[u]; ~i; i = nx[i]){
46             if(w[i] > 0 && deep[to[i]] == 0){
47                 deep[to[i]] = deep[u] + 1;
48                 q.push(to[i]);
49             }
50         }
51     }
52     if(deep[t] > 0) return 1;
53     return 0;
54 }
55 int Dinic(int u, int flow){
56     if(u == t) return flow;
57     for(int i = head[u]; ~i; i = nx[i]){
58         if(deep[u]+1 == deep[to[i]] && w[i] > 0){
59             int di = Dinic(to[i], min(w[i], flow));
60             if(di > 0){
61                 w[i] -= di, w[i^1] += di;
62                 return di;
63             }
64         }
65     }
66     return 0;
67 }
68 int main(){
69     while(~scanf("%d%d", &m, &n)){
70         init();
71         for(int i = 1; i <= m; i++){
72             scanf("%d%d%d", &_u, &_v, &_w);
73             add(_u, _v, _w);
74             add(_v, _u, 0);
75         }
76         s = 1; t = n;
77         int ans = 0, tmp;
78         while(bfs()){
79             while(tmp = Dinic(s, INF)) ans += tmp;
80         }
81         printf("%d\n", ans);
82     }
83     return 0;
84 }

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。

 

 1 #include
 2 using namespace std;
 3 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 4 #define LL long long
 5 #define ULL unsigned LL
 6 #define fi first
 7 #define se second
 8 #define pb push_back
 9 #define lson l,m,rt<<1
10 #define rson m+1,r,rt<<1|1
11 #define max3(a,b,c) max(a,max(b,c))
12 #define min3(a,b,c) min(a,min(b,c))
13 #define _S(X) cout << x << ' ';
14 #define __S(x) cout << x << endl;
15 typedef pair<int,int> pll;
16 const int INF = 0x3f3f3f3f;
17 const LL mod =  (int)1e9+7;
18 const int N = 405;
19 int head[N], w[N], to[N], nx[N];
20 int n, m, _u, _v, _w;
21 int tot, s, t;
22 int deep[N], cur[N];
23 void add(int u, int v, int val){
24     w[tot]  = val;
25     to[tot] = v;
26     nx[tot] = head[u];
27     head[u] = tot++;
28 }
29 
30 void init(){
31     memset(head, -1, sizeof(head));
32     tot = 0;
33     s = 1;
34     t = n;
35 }
36 
37 int bfs(){
38     queue<int> q;
39     memset(deep, 0, sizeof(deep));
40     q.push(s);
41     deep[s] = 1;
42     while(!q.empty()){
43         int u = q.front();
44         q.pop();
45         for(int i = head[u]; ~i; i = nx[i]){
46             if(w[i] > 0 && deep[to[i]] == 0){
47                 deep[to[i]] = deep[u] + 1;
48                 q.push(to[i]);
49             }
50         }
51     }
52     if(deep[t] > 0) return 1;
53     return 0;
54 }
55 int Dinic(int u, int flow){
56     if(u == t) return flow;
57     for(int &i = cur[u]; ~i; i = nx[i]){
58         if(deep[u]+1 == deep[to[i]] && w[i] > 0){
59             int di = Dinic(to[i], min(w[i], flow));
60             if(di > 0){
61                 w[i] -= di, w[i^1] += di;
62                 return di;
63             }
64         }
65     }
66     return 0;
67 }
68 int main(){
69     while(~scanf("%d%d", &m, &n)){
70         init();
71         for(int i = 1; i <= m; i++){
72             scanf("%d%d%d", &_u, &_v, &_w);
73             add(_u, _v, _w);
74             add(_v, _u, 0);
75         }
76         s = 1; t = n;
77         int ans = 0, tmp;
78         while(bfs()){
79             for(int i = 1; i <= n; i++) cur[i] = head[i];
80             while(tmp = Dinic(s, INF)) ans += tmp;
81         }
82         printf("%d\n", ans);
83     }
84     return 0;
85 }

当前弧优化

 1 #include
 2 using namespace std;
 3 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 4 #define LL long long
 5 #define ULL unsigned LL
 6 #define fi first
 7 #define se second
 8 #define pb push_back
 9 #define lson l,m,rt<<1
10 #define rson m+1,r,rt<<1|1
11 #define max3(a,b,c) max(a,max(b,c))
12 #define min3(a,b,c) min(a,min(b,c))
13 #define _S(X) cout << x << ' ';
14 #define __S(x) cout << x << endl;
15 typedef pair<int,int> pll;
16 const int INF = 0x3f3f3f3f;
17 const LL mod =  (int)1e9+7;
18 const int N = 405;
19 int head[N], w[N], to[N], nx[N];
20 int vis[N], pre[N], id[N];
21 int n, m, _u, _v, _w;
22 int tot, s, t;
23 void add(int u, int v, int val){
24     w[tot]  = val;
25     to[tot] = v;
26     nx[tot] = head[u];
27     head[u] = tot++;
28 }
29 
30 void init(){
31     memset(head, -1, sizeof(head));
32     tot = 0;
33     s = 1;
34     t = n;
35 }
36 
37 int bfs(){
38     queue<int> q;
39     memset(vis, 0, sizeof(vis));
40     q.push(s);
41     vis[s] = 1;
42     pre[s] = s;
43     while(!q.empty()){
44         int u = q.front();
45         q.pop();
46         for(int i = head[u]; ~i; i = nx[i]){
47             if(!vis[to[i]] && w[i]){
48                 pre[to[i]] = u;
49                 id[to[i]] = i;
50                 vis[to[i]] = 1;
51                 if(to[i] == t) return true;
52                 q.push(to[i]);
53             }
54         }
55     }
56     return false;
57 }
58 int EK(){
59     int ans = 0;
60     while(bfs()){
61         int mi = INF;
62         for(int i = t; i != s; i = pre[i]){
63             mi = min(mi, w[id[i]]);
64         }
65         for(int i = t; i != s; i = pre[i]){
66             w[id[i]] -= mi;
67             w[id[i]^1] += mi;
68         }
69         ans += mi;
70     }
71     return ans;
72 }
73 int main(){
74     while(~scanf("%d%d", &m, &n)){
75         init();
76         for(int i = 1; i <= m; i++){
77             scanf("%d%d%d", &_u, &_v, &_w);
78             add(_u, _v, _w);
79             add(_v, _u, 0);
80         }
81         s = 1; t = n;
82         printf("%d\n", EK());
83     }
84     return 0;
85 }

EK

 

转载于:https://www.cnblogs.com/MingSD/p/9297759.html