【最大流之EdmondsKarp算法】【HDU1532】模板题

题意：裸的最大流，什么是最大流，参考别的博客

运用复杂度最高的EK算法 O（M*N),模板来自紫书

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <ctime>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <queue>
#define INF 0x3f3f3f3f
#define oo 0x13131313
const int maxn=200+5;
using namespace std;
struct Edge {
    int from,to,cap,flow;
    Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){}
};
struct EdmondsKarp{
    int n,m;
    vector<Edge> edges; //边集数组，边数*2
    vector<int> G[maxn]; //邻接表
    int a[maxn];        //起点到i的可改进量
    int p[maxn];        //最短路树上p的弧编号
    void init(int n){
    for(int i = 0;i < n; i++) G[i].clear();
    edges.clear();
    }
    void AddEdge(int from,int to,int cap){
    edges.push_back(Edge(from,to,cap,0));
    edges.push_back(Edge(to,from,0,0));  //反向弧
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
    }

    int Maxflow(int s,int t)
    {
        int flow=0;
        for(;;){
            memset(a,0,sizeof(a));
            queue<int> Q;
        //    while(!Q.empty()) Q.pop();
            Q.push(s);
            a[s]=INF;
            while(!Q.empty()) {
                int x=Q.front();Q.pop();
                for(int i=0;i<G[x].size();i++) {
                    Edge &e=edges[G[x][i]];
                    if(!a[e.to]&&(e.cap>e.flow)) {
                        p[e.to]=G[x][i];
                        a[e.to]=min(a[x],e.cap-e.flow);
                        Q.push(e.to);
                    }
                }
                if(a[t]) break;
            }
            if(!a[t]) break;
            for(int u=t;u!=s;u=edges[p[u]].from){
                edges[p[u]].flow+=a[t];
                edges[p[u]^1].flow-=a[t];

            }
            flow+=a[t];
        }
        return flow;
    }
};

完整代码：

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <ctime>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <queue>
#define INF 0x3f3f3f3f
#define oo 0x13131313
const int maxn=200+5;
using namespace std;
struct Edge {
    int from,to,cap,flow;
    Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){}
};
struct EdmondsKarp{
    int n,m;
    vector<Edge> edges; //边集数组，边数*2
    vector<int> G[maxn]; //邻接表
    int a[maxn];        //起点到i的可改进量
    int p[maxn];        //最短路树上p的弧编号
    void init(int n){
    for(int i = 0;i < n; i++) G[i].clear();
    edges.clear();
    }
    void AddEdge(int from,int to,int cap){
    edges.push_back(Edge(from,to,cap,0));
    edges.push_back(Edge(to,from,0,0));  //反向弧
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
    }

    int Maxflow(int s,int t)
    {
        int flow=0;
        for(;;){
            memset(a,0,sizeof(a));
            queue<int> Q;
        //    while(!Q.empty()) Q.pop();
            Q.push(s);
            a[s]=INF;
            while(!Q.empty()) {
                int x=Q.front();Q.pop();
                for(int i=0;i<G[x].size();i++) {
                    Edge &e=edges[G[x][i]];
                    if(!a[e.to]&&(e.cap>e.flow)) {
                        p[e.to]=G[x][i];
                        a[e.to]=min(a[x],e.cap-e.flow);
                        Q.push(e.to);
                    }
                }
                if(a[t]) break;
            }
            if(!a[t]) break;
            for(int u=t;u!=s;u=edges[p[u]].from){
                edges[p[u]].flow+=a[t];
                edges[p[u]^1].flow-=a[t];

            }
            flow+=a[t];
        }
        return flow;
    }
};
EdmondsKarp A;
int N;
void File()
{
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
}
void input()
{
    int a,b,c;
    for(int i=1;i<=N;i++)
    {
        scanf("%d%d%d",&a,&b,&c);
        A.AddEdge(a,b,c);
    }
}
void solve()
{
    int ans=0;
    ans=A.Maxflow(1,A.n);
    printf("%d
",ans);
}
int main()
{
  //  File();
    A.init(maxn);
    while(scanf("%d%d",&N,&A.n)!=EOF)
    {
        input();
        solve();
        A.init(maxn);           //注意用maxn 去初始化！
    }
    return 0;
}