http://poj.org/problem?id=1273
增广路算法。
Ford_Fullkerson
1 /* 2 Author:Zhaofa Fang 3 Lang:C++ 4 */ 5 #include <cstdio> 6 #include <cstdlib> 7 #include <iostream> 8 #include <cmath> 9 #include <cstring> 10 #include <algorithm> 11 #include <string> 12 #include <utility> 13 #include <vector> 14 #include <queue> 15 #include <stack> 16 #include <map> 17 #include <set> 18 using namespace std; 19 20 typedef long long ll; 21 const int INF = 2147483647; 22 23 struct Edge 24 { 25 int v,c,next; 26 }edge[1005]; 27 int eh[505],pp; 28 int pre[505]; 29 int G[505][505]; 30 void init() 31 { 32 pp = 0; 33 memset(eh,-1,sizeof(eh)); 34 memset(G,0,sizeof(G)); 35 } 36 void add(int u,int v,int c) 37 { 38 edge[pp].v=v; 39 edge[pp].c=c; 40 edge[pp].next=eh[u]; 41 eh[u]=pp++; 42 } 43 void addedge(int u,int v,int c) 44 { 45 add(u,v,c); 46 G[u][v]+=c; 47 add(v,u,0); 48 G[v][u]+=0; 49 } 50 int bfs(int s,int t) 51 { 52 queue<int> q; 53 bool vist[505]; 54 memset(vist,0,sizeof(vist)); 55 q.push(s); 56 vist[s]=1; 57 while(!q.empty()) 58 { 59 int now=q.front();q.pop(); 60 for(int i=eh[now];i!=-1;i=edge[i].next) 61 { 62 int v=edge[i].v; 63 if(G[now][v] > 0 && !vist[v]) 64 { 65 vist[v]=1; 66 pre[v]=now; 67 if(v == t)return 1; 68 q.push(v); 69 } 70 } 71 } 72 return 0; 73 } 74 int Ford_Fullkerson(int s,int t,int &F) 75 { 76 memset(pre,0,sizeof(pre)); 77 int min=INF; 78 if(bfs(s,t) == 0)return 0; 79 for(int i=t;i!=s;i=pre[i]) 80 { 81 if(G[pre[i]][i] < min)min=G[pre[i]][i]; 82 } 83 for(int i=t;i!=s;i=pre[i]) 84 { 85 G[pre[i]][i] -= min; 86 G[i][pre[i]] += min; 87 } 88 F += min; 89 return 1; 90 } 91 int main() 92 { 93 #ifndef ONLINE_JUDGE 94 freopen("in","r",stdin); 95 #endif 96 int m,n; 97 while(~scanf("%d%d",&m,&n)) 98 { 99 int u,c,v; 100 init(); 101 while(m--) 102 { 103 scanf("%d%d%d",&u,&v,&c); 104 addedge(u,v,c); 105 } 106 int F = 0; 107 while(Ford_Fullkerson(1,n,F)); 108 cout<<F<<endl; 109 } 110 return 0; 111 }
sap_gap.
1 /* 2 Author:Zhaofa Fang 3 Lang:C++ 4 */ 5 #include <cstdio> 6 #include <cstdlib> 7 #include <iostream> 8 #include <cmath> 9 #include <cstring> 10 #include <algorithm> 11 #include <string> 12 #include <vector> 13 #include <queue> 14 #include <stack> 15 #include <map> 16 #include <set> 17 using namespace std; 18 19 typedef long long ll; 20 const int INF = 2147483647; 21 22 struct edge 23 { 24 int u,v; 25 int cap,flow; 26 int next; 27 }; 28 int eh[505],tot; 29 edge et[505<<1]; 30 void add(int u,int v,int cap,int flow) 31 { 32 edge E={u,v,cap,flow,eh[u]}; 33 et[tot]=E,eh[u]=tot++; 34 } 35 void addedge(int u,int v,int cap) 36 { 37 add(u,v,cap,0);add(v,u,0,0); 38 } 39 int cur[505],cnt[505],dist[505],pre[505]; 40 int low[505]; 41 int sap_gap(int s,int t,int n) 42 { 43 int u,v,now; 44 memset(dist,0,sizeof(dist)); 45 memset(low,0,sizeof(low)); 46 for(u=0;u<=n;u++)cur[u] = eh[u]; 47 int flow=0; 48 u = s; 49 low[s] = INF;cnt[0] = n; 50 while(dist[s] < n) 51 { 52 for(now = cur[u];now != -1;now = et[now].next) 53 if(et[now].cap - et[now].flow && dist[u] == dist[v = et[now].v] + 1)break; 54 if(now != -1) 55 { 56 cur[u] = now;pre[v] = now; 57 low[v] = et[now].cap - et[now].flow; 58 low[v] = min(low[v],low[u]); 59 u = v; 60 if(u == t) 61 { 62 for(;u != s;u = et[pre[u]].u) 63 { 64 et[pre[u]].flow += low[t]; 65 et[pre[u]^1].flow -= low[t]; 66 } 67 flow += low[t];low[s] = INF; 68 } 69 } 70 else 71 { 72 if(--cnt[dist[u]] == 0)break; 73 dist[u] = n;cur[u] = eh[u]; 74 for(now = eh[u];now != -1;now = et[now].next) 75 if(et[now].cap-et[now].flow > 0 && dist[u] > dist[et[now].v] + 1) 76 dist[u] = dist[et[now].v] + 1; 77 cnt[dist[u]]++; 78 if(u != s)u = et[pre[u]].u; 79 } 80 } 81 return flow; 82 } 83 int n,m; 84 void init() 85 { 86 tot = 0; 87 memset(eh,-1,sizeof(eh)); 88 } 89 90 int main() 91 { 92 #ifndef ONLINE_JUDGE 93 freopen("in","r",stdin); 94 #endif 95 int a,b,c; 96 while(~scanf("%d%d",&m,&n)) 97 { 98 init(); 99 for(int i=1;i<=m;i++) 100 { 101 scanf("%d%d%d",&a,&b,&c); 102 addedge(a,b,c); 103 104 } 105 printf("%d\n",sap_gap(1,n,n)); 106 } 107 return 0; 108 }
Dinic.O(V*V*E)
1 Source Code 2 3 Problem: 1273 User: qq6616323 4 Memory: 716K Time: 0MS 5 Language: G++ Result: Accepted 6 Source Code 7 /* 8 *Author: Zhaofa Fang 9 *Created time: 2013-07-13-10.25 10 *Language: C++ 11 */ 12 #include <cstdio> 13 #include <cstdlib> 14 #include <sstream> 15 #include <iostream> 16 #include <cmath> 17 #include <cstring> 18 #include <algorithm> 19 #include <string> 20 #include <utility> 21 #include <vector> 22 #include <queue> 23 #include <map> 24 #include <set> 25 using namespace std; 26 27 typedef long long ll; 28 #define DEBUG(x) cout<< #x << ':' << x << endl 29 #define FOR(i,s,t) for(int i = (s);i <= (t);i++) 30 #define FORD(i,s,t) for(int i = (s);i >= (t);i--) 31 #define REP(i,n) for(int i=0;i<(n);i++) 32 #define REPD(i,n) for(int i=(n-1);i>=0;i--) 33 #define PII pair<int,int> 34 #define PB push_back 35 #define MP make_pair 36 #define ft first 37 #define sd second 38 #define lowbit(x) (x&(-x)) 39 #define INF (1<<30) 40 #define eps 1e-8 41 42 const int maxn = 505; 43 const int maxm = 1010; 44 struct Edge{ 45 int v,cap,flow,next; 46 }edge[maxm]; 47 int eh[maxn],tot; 48 int d[maxn]; 49 bool vist[maxn]; 50 51 void init(){ 52 tot = 0; 53 memset(eh,-1,sizeof(eh)); 54 } 55 void addedge(int u,int v,int c,int f){ 56 Edge e = {v,c,f,eh[u]}; 57 edge[tot] = e; 58 eh[u] = tot ++; 59 } 60 void add(int u,int v,int c,int f){ 61 addedge(u,v,c,f); 62 addedge(v,u,f,0); 63 } 64 65 bool BFS(int s,int t){ 66 memset(vist,0,sizeof(vist)); 67 queue<int>Q; 68 Q.push(s); 69 d[s] = 0; 70 vist[s] = 1; 71 while(!Q.empty()){ 72 int u = Q.front(); 73 Q.pop(); 74 for(int i=eh[u];i!=-1;i=edge[i].next){ 75 int v = edge[i].v; 76 if(!vist[v] && edge[i].cap>edge[i].flow){ 77 vist[v] = 1; 78 d[v] = d[u] + 1; 79 Q.push(v); 80 } 81 } 82 } 83 return vist[t]; 84 } 85 int DFS(int u,int t,int avi){ 86 if(u == t || avi == 0)return avi; 87 int flow = 0 , f; 88 for(int i=eh[u];i!=-1;i=edge[i].next){ 89 int v = edge[i].v; 90 if(d[u] + 1 == d[v] && (f=DFS(v,t,min(avi,edge[i].cap-edge[i].flow)))>0){ 91 edge[i].flow += f; 92 edge[i^1].flow -= f; 93 flow += f; 94 avi -= f; 95 if(avi == 0)break; 96 } 97 } 98 return flow; 99 } 100 int maxFlow(int s,int t){ 101 int flow = 0; 102 while(BFS(s,t)){ 103 flow += DFS(s,t,INF); 104 } 105 return flow; 106 } 107 int main(){ 108 //freopen("in","r",stdin); 109 //freopen("out","w",stdout); 110 int n,m; 111 while(~scanf("%d%d",&n,&m)){ 112 int u,v,c; 113 init(); 114 while(n --){ 115 scanf("%d%d%d",&u,&v,&c); 116 add(u,v,c,0); 117 } 118 printf("%d\n",maxFlow(1,m)); 119 } 120 return 0; 121 }