网络流Ford-Fulkerson模板代码:
#include
#include
#include
#include
using namespace std;
const int N = 250;
const int INF = 0x3f3f3f3f;
struct Node
{
int to;
int cap;
int rev;
};
vector v[N];
bool used[N];
void add_Node(int from, int to, int cap)
{
v[from].push_back((Node){to, cap, v[to].size()});
v[to].push_back((Node){from, 0, v[from].size() - 1}); //相当于前向星
}
int dfs(int s, int t, int f)
{
if(s == t)
return f;
used[s] = true;
for(int i = 0; i < v[s].size(); i++)
{
Node &tmp = v[s][i];
if(used[tmp.to] == false && tmp.cap > 0)
{
int d = dfs(tmp.to, t, min(f, tmp.cap));
if(d > 0)
{
tmp.cap -= d;
v[tmp.to][tmp.rev].cap += d;
return d;
}
}
}
return 0;
}
int max_flow(int s, int t)
{
int flow = 0;
for(;;)
{
memset(used, false, sizeof(used));
int f = dfs(s, t, INF);
if(f == 0)
return flow;
flow += f;
}
}
int main()
{
int n, m;
while(~scanf("%d%d", &n, &m))
{
memset(v, 0, sizeof(v));
for(int i = 0; i < n; i++)
{
int x, y, z;
scanf("%d%d%d", &x, &y, &z);
add_Node(x, y, z);
}
printf("%d\n", max_flow(1, m));
}
return 0;
}
Dinic模板:
#include
#include
#include
using namespace std;
int n, m, maxflow;//n点数, m边数
int edge[250][250];//邻接矩阵
int dis[250];//距源点的距离,分层图
int q[250];//BFS队列
int BFS()
{
int u, v;
memset(dis, -1, sizeof(dis));
dis[1] = 0;
int head = 0, tail = 1;
q[1] = 1;
while(head < tail)
{
u = q[++head];
for(int v = 1; v <= n; v++)
if(dis[v] < 0 && edge[u][v] > 0)
{
dis[v] = dis[u] + 1;
q[++tail] = v;
}
}
if(dis[n] > 0)
return 1;
else
return 0;//汇点的DIS小于零,表明BFS不到汇点
}
//dinic代表一次增广,函数返回本次增广的流量,返回0表示无法增广
int dinic(int u, int low)Low是源点到现在最窄的(剩余流量最小)的边的剩余流量
{
int flow;
if(u == n)//是汇点
return low;
for(int v = 1; v <= n; v++)
if(edge[u][v] > 0 && dis[v] == dis[u] + 1 && (flow = dinic(v, min(low, edge[u][v]))))//联通且是分层图的下一层且能到汇点(flow <> 0)
{
edge[u][v] -= flow;
edge[v][u] += flow;
return flow;
}
return 0;
}
int main()
{
int u, v, w, flow;
while(scanf("%d%d", &m, &n) != EOF)
{
memset(edge, 0, sizeof(edge));
for(int i = 1; i <= m; i++)
{
scanf("%d%d%d", &u, &v, &w);
edge[u][v] += w;
}
maxflow = 0;
while(BFS())//要不停地建立分层图,如果BFS不到汇点才结束
{
while(flow = dinic(1, 0x3f3f3f3f))//一次BFS要不停地找增广路,直到找不到为止
maxflow += flow;
}
printf("%d\n", maxflow);
}
return 0;
}